High speed X-ray microscope

ABSTRACT

A high resolution x-ray microscope with a high flux x-ray source that allows high speed metrology or inspection of objects such as integrated circuits (ICs), printed circuit boards (PCBs), and other IC packaging technologies. The object to be investigated is illuminated by collimated, high-flux x-rays from a movable, extended source having a designated x-ray spectrum. The system also comprises a means to control the relative positions of the x-ray source and the object; a scintillator that absorbs x-rays and emits visible photons positioned in very close proximity to (or in contact with) the object; an optical imaging system that forms a highly magnified, high-resolution image of the photons emitted by the scintillator; and a detector such as a CCD array to convert the image to electronic signals.

RELATED INVENTIONS

The present application is a Continuation of U.S. patent applicationSer. No. 14/732,674, filed Jun. 6, 2015 and entitled DEVICES PROCESSED USING X-RAYS, which is a continuation of U.S. patent application Ser. No.13/987,808, filed Sep. 4, 2013 and entitled HIGH SPEED X-RAY INSPECTIONMICROSCOPE, which in turn claims the benefit of U.S. ProvisionalApplication No. 61/743,458, filed on Sep. 5, 2012 and entitled X-RAYINSPECTION MICROSCOPE, and also claims the benefit of U.S. ProvisionalApplication No. 61/852,061, filed on Mar. 15, 2013 and entitled X-RAYINSPECTION MICROSCOPE, both of which are herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to the high-speed examination and inspection ofobjects using x-rays that have structures of interest on the micrometerto nanometer scale. Such objects include integrated circuits (ICs) andintegrated circuit packaging, including multi-chip packages (MCPs) withsilicon interposers and through-silicon vias (TSVs). Certain naturalobjects (crystals or quasi-crystals) or biological structures may alsobe examined using these techniques.

In particular, this high-speed examination and inspection isaccomplished by illuminating the object with x-rays, and using ascintillator to convert the transmitted high-resolution x-ray patterninto a high-resolution visible light image. The high-resolution visiblelight images are then relayed onto a sensor, such as a charge-coupleddevice (CCD) camera, where they are converted into electronic signals.

Once the image has been captured electronically, it can be used as amicroscope image for metrology and structural analysis. Dimensions, suchas “critical dimensions” (CDs) for integrated circuit structures, can bedetermined by analysis of the images. Multiple images can be combined todetermine 2-dimensional (2D) and 3-dimensional (3D) structures and theirmeasurements. Due to the high-speed acquisition of the image enabled bythis invention, these measurements can be used for in-process metrology,sampling either the incoming material for a manufacturing process, oritems at various stages of the manufacturing process, for qualitycontrol. It can also be used for metrology after manufacturing has beencompleted, to ensure manufacturing specifications have been met.

High-speed metrology is the backbone of statistical process control, orSPC. SPC improves yield over simple inspection by identifying productionvariations before they cause a loss of product yield. In order to obtainproduct yields over 90%, it is often necessary to closely monitorvariations in production that are not necessarily defects, but indicateprocess variations that can lead to defects. Using SPC it is possible tomaintain very high yields.

The presence of defects within the structure can also be observed fromthe images, and the image can therefore be used for inspection ofobjects and for manufacturing process control. Defects can be detectedmanually, or by comparison with other areas within the object, or bycomparison with stored information such as an image of a device known tobe correctly manufactured. The invention can be used for detectingdefects (inspection), determining the location of suspected defects(defect location) or determining the cause of known defects (failureanalysis).

The high-speed metrology and inspection results can in turn be used foryield analysis of manufacturing processes (such as the fabrication ofintegrated circuits and other semiconductor devices), as well as forpackaging technologies for those devices (such as interposers withthrough-silicon vias (TSVs), or multi-chip packaging (MCP) processessuch as those using microbumping for assembling multiple chips into onepackage). The yield analysis results can in turn be used to improveyield for these and other manufacturing and packaging processes.

BACKGROUND OF THE INVENTION

Since the early days of the semiconductor industry, the observationknown as “Moore's Law” has been followed by the industry. This “law”states that the number of transistors that can economically beintegrated into a semiconductor device increases by a factor of 1.5 to2.0 times every two years. The increase has generally been achieved byminiaturization of the components of the electronic device, achievedthrough planer scaling of the transistor and interconnect wiring, andhas provided the additional benefits of continuous improvements inprocessing power, data storage density and functional integration ofsemiconductor devices and the end products of which they are criticalcomponents. The current state-of-the-art semiconductor devices are builtusing a minimum critical dimension of about 28 nanometers, and smallerdevices are in development.

In order to reduce the size of transistors and continue to improvesemiconductor performance, it is necessary to create patterns on thesilicon substrate in ever decreasing dimensions. Photolithography is themost common process used to create these patterns. The minimum featuresize that can be lithographically patterned is generally limited to afactor of the wavelength of the illumination source. The state of theart illumination source used in lithographic manufacturing today usesillumination at a wavelength of 193 nanometers. In order to produce 28nanometer features, a number of improvements have been employed,including the use of immersion optics to increase the numerical aperture(NA) of the lithographic system, the use of design modifications for thephotomask, sometimes called optical proximity correction (OPC), toimprove final image fidelity, and the use of multiple photo-exposuresfor patterning a single layer. These techniques, while makingsub-wavelength patterning possible, add significant cost to the process.

Although single functional transistors with gate dimensions as small as5 nm in size have been demonstrated, and manufacturing techniques havebeen proposed to enable large-scale patterning for devices withdimensions smaller than 10 nm, the cost effectiveness and commercialfeasibility of these solutions have yet to be demonstrated.

An alternative to device shrinking that can enable the functionalintegration of ever greater numbers of semiconductor devices in a costeffective manner is the utilization of techniques that connectintegrated devices vertically. New methods of attaching integratedcircuits (ICs) to each other and to printed circuit boards (PCBs) arenow being introduced. These new methods include silicon interposers andthrough-silicon vias (TSVs), so-called “3D IC” and “2.5D IC”technologies. The interconnections used for 3D and 2.5D packagingbetween stacked IC or semiconductor devices are much smaller than forPCBs. While PCBs rarely use interconnections smaller than a 50 micronminimum pitch dimension, commercial TSV packages can have diameters assmall as 2 microns, and silicon interposers can have features withdimensions below 100 nanometers. Interposers can also be manufacturedfrom glass, or a composite of organic material with fiberglass or aparticle filler such as silica.

Integrated circuits are often manufactured using custom processes,depending on the device being manufactured. For example, dynamicrandom-access memory (DRAM) chips may require a different process recipethan complementary metal-oxide-semiconductor (CMOS) logic chips if eachis to be manufactured for optimum performance. In the past, if a devicethat needed both memory and logic was desired, a chip design using bothin the same IC could be manufactured, but with a compromise thatoptimized the performance of neither logic nor memory. Alternatively, aprinted circuit board (PCB) could be manufactured, containing both amemory and a logic chip, each manufactured for optimum performance.However, the long distances that the signals would have to travel on thePCB from chip-to-chip will slow the performance considerably. As theclock speed of logic chips has increased and multiple operating coreshave been introduced, memory-access latency resulting from traditionalsurface mount, through-hole interconnect, ball grid arrays (BGAs), ordual in-line memory module (DIMMs) on printed circuit boards has begunto limit the performance of more and more electronic systems.

Recently, it is becoming popular to stack ICs and connect them withinthe same package. One example of this new packaging technology is thesilicon interposer that provides interconnection between two or moresemiconductor devices, a semiconductor device and a printed circuitboard, or a semiconductor device and some other package component. Anactive silicon device may also function as an interposer in which casethe structure is typically referred to as “3D IC”. The interposer istypically a layer of silicon, manufactured from the same kind of siliconwafer used for the ICs themselves, in which vias that pass through thesilicon have been manufactured. The vias, placed at predeterminedlocations, are holes filled with an electrically conducting material(such as copper (Cu)) that pass completely through the silicon. Whenchips are bonded to both sides of the interposer, the through-siliconvias (TSVs) allow signals from one IC to travel a relatively shortdistance vertically from one chip to another. When chips are bonded to aPCB using an interposer, they allow signals from the chips on one sideof the interposer to connect the PCB.

Similar interposers with vias passing through the materials may also befabricated using glass or a reinforced organic material.

These vias are typically made of copper (Cu), but processes using viasmade of tungsten (W) have also been developed, and vias with a varietyof metal layers are anticipated. Interposers with thickness of less than50 microns with via diameters of about 5 microns have been demonstrated.Somewhat thicker interposers may be desirable for some manufacturingprocesses, but the thickness is typically limited by the practical ofheight to via diameter aspect ratio that can be reliably manufactured.Aspect ratio of 10:1 has been widely demonstrated and prototypesindicate aspect ratios of 20:1 are possible. A single interposer,serving as the interconnection between memory chips that can containbillions of memory cells and a logic chip for a microprocessor, can havethousands or even tens of thousands of TSVs. For thinner interposers,smaller TSV diameters (as small as 1 micron) have been proposed,allowing an even greater number of connections. Since each TSV is avital communication link between a portion of the logic and memory chip,each TSV must function perfectly. No breakdown in communication can beallowed.

It is therefore imperative that, before the active chips are bondedtogether to the interposer, the interposer is known to be 100%functional. The economic need for this is clear—bonding good chips to abad interposer ruins all the economic value invested in making thechips.

There is therefore a need to properly test and/or inspect theseinterposers before final bonding takes place.

Aside from interposers with TSVs, other packaging technologies are alsobeing explored as a way to increase the number of transistors in asingle package, and continue the benefits of Moore's Law.

Flip chip interconnect (FCI), sometimes called controlled collapse chipconnection (or “C4”), is one such technology that is currently beingused. In this process, a pad ring is connected to rows, columns or anarray of solder bumps on the surface of a chip while it is still in theform of a wafer. The bumps may form an array on the surface of the chip,a partial array, or may exist in a single perimeter row around the chipor a column in the center or side. The bumps are may be aligned toeither the package substrate or to another die.

In traditional processes, the individual chips are then “diced” orsingulated from the wafer and placed onto a substrate which is typicallycomposed of glass fiber reinforced epoxy (such as FR4), bismaleimidetriazine (BT) or similar, but may also be ceramic or Teflon or otherstable material, or even a flexible substrate such as tape. Solder fluxmay be first applied to the bump and or substrate contact surface or itmay be a component of the solder paste applied during the process.

The bumped chip and substrate are passed through a mass reflow furnace.During this process the solder melts and re-solidifies. This melting andre-solidifying should produce the desired outcome of a reliableconnection at each joint between every micro-bump and every land, pad orterminal on the associated substrate or die. Chips with about 2,000bumps using this process have been demonstrated. The pitch of such bumparrays is typically larger than 100 microns.

After mass reflow, the solder joints created in this process may beinspected using acoustic microscopy. A sound wave is passed through thejoint and either detected on the other side of the structure orreflected back to the sending side. Changes in the properties of theacoustic signal can be utilized to determine if the solder joint isnormal or not.

This kind of immediate feedback provided by acoustic microscopy allowsfor rapid identification of problems and their correction bymodification of the process, materials, and equipment used in themanufacture of such products.

Newer products are currently entering the market that requireinterconnect pitches of less than 100 microns. Single perimeter rows ofbumps made from copper and attached to organic substrates have beendemonstrated at a pitch of 50 microns, and dual rows of copper bumpsattached to organic substrates have been demonstrated at a pitch of 80microns. These chips are typically mounted to the substrate using aprocess known as thermo-compression bonding. As opposed to mass reflow,in thermo compression bonding, the bumped chip is aligned to thesubstrate, placed onto the substrate and then exposed to pressure andheat all using a single tool. Typically one chip is processed at a time,and processing times can exceed tens of seconds for each individualchip.

Newer products such as those applying silicon or other fine pitchinterposers or 3D stacking of die onto active devices require a fullarray of contacts at pitches of 50 microns or smaller. The demands foreven smaller and smaller pitch is expected to continue as chip to chipdata rates expand.

For current parts being developed at this smaller bump pitch, there isno reliable non-destructive test methodology to inspect the quality ofbonds formed during the bonding process. Acoustic microscopy has notdemonstrated the ability to detect flaws in solder bumps at bump pitchesof 50 microns and below. And, in many cases, the electrical contactpoints on the parts are too small even for electrical testing at thisstage in the manufacturing process. So additional manufacturing stepsmust be performed at additional cost. In most cases, several days orweeks may be required until an electrical test is performed on anassembled package.

In many cases, due to the lack of feedback data during package assemblyor bonding process, some or all of the units tested will be found to benon-functional. Current failure analysis techniques examine these failedparts mechanically, typically by using focused ion beam milling tolocate the specific failed connection. The connection thus exposed canbe imaged used existing scanning electron microscope techniques. Thetime required to create an image of a defected bond has been reported tobe in the range of 1-2 weeks after electrical test due to the difficultyand time required to mill to the specific spot in question without goingthrough or past it. This is unacceptable for high-speed production linesor package assembly.

There is therefore a need for a failure analysis technique that cannon-destructively examine failed parts for process improvement,preferably in a matter of seconds, and then be used in a manufacturingline for statistical process control (SPC).

For the prior art testing of interposers, electrical probes can be usedto make continuity tests of the TSVs. However, given that there may betens of thousands of TSVs, a probe using tens of thousands of electrodesmay be required. It is unclear if such a probe is even possible usingstandard testing techniques. Furthermore, such probes physically touchthe ends of the TSVs, and must be jammed against the surface to insuregood electrical continuity. This protocol may in fact leave what was aperfectly good interposer scratched and marred by the time the test isfinished, while not revealing this in the data gathered by the probewhile it was in contact.

The pitch of connections on an interposer or die is also smaller thanconventional devices being either probed or contacted. Even at thecurrent level of technology, mechanical contact by probes or contactssmall enough for the next generation of TSVs, flip chip bumpers, orinterposers is not readily available to accomplish such an electricaltest.

In addition, many interposers have electrical connection between the topside and the bottom side of the interposer. Contact with probes wouldhave to be to both sides of the interposer. This further increases thedifficulty of manufacturing an electrical test mechanism for siliconinterposers.

In IC manufacturing, inspection to confirm correct, defect-freemanufacturing is routinely used to examine wafers and PCBs beforeproceeding to the next manufacturing step. Integrated circuits (ICs) areinspected at many steps in the process, from bare wafer inspection toinspecting printed circuit boards (PCBs) before and after attaching ICs.Different types of microscopes are used at different inspection points:electron and optical microscopes are often used for inspecting the ICsduring the manufacturing process, and x-ray microscopes can be used forinspecting PCBs.

The inspection techniques using optical photons or electrons to inspectsilicon wafers cannot be used to inspect 3D and 2.5D IC packages becausethey do not penetrate through the ICs or interposers sufficiently toprovide an internal view of the packaged ICs. They are also not capableof performing inspection or metrology for partially packaged components,a critical requirement for process control. X-rays, however, canpenetrate through many layers of packaging to provide an internal viewof the assembled device.

The initial discovery of x-rays by Röntgen in 1895 [W. C. Röntgen, “EineNeue Art von Strahlen (Würzburg Verlag, 1895); “On a New Kind of Rays,”Nature, Vol. 53, pp. 274-276 (Jan. 23 1896)] was in the form ofshadowgraphs, in which the contrast of x-ray transmission for biologicalsamples (e.g. bones vs. tissue) allowed internal structures to berevealed without damaging the samples themselves. However, because oftheir short wavelength (10 to 0.01 nm, corresponding to energies in therange of 100-100,000 eV), and the absence of materials for which therefractive index for x-rays differs significantly from 1, there are noeasy equivalents to refractive or reflective optical elements socommonly used in optical system design. So, even now, the most commonuse of x-rays is still as a simple shadowgraph, observing the structureof bones and teeth in the offices of doctors and dentists.

Early x-ray “microscopy,” developed more than 50 years after the initialdiscovery of x-rays, simply consisted of elaborate shadowgraphapparatus, in which the diverging x-rays cast a shadow larger than theobject [S. P. Newberry and S. E. Summers, U.S. Pat. No. 2,814,729]. Withthe advent of computer data collection, it became possible to gathermore information from the specimen, changing the relative positions andillumination angles of the x-ray source and specimen in a systematicway. Using multiple transmission measurements taken at multiple anglesaround the specimen, images can be synthesized by computer thatrepresent a 2-dimensional or 3-dimensional model of the specimen [G. N.Hounsfield, U.S. Pat. No. 3,778,614]. The “slices” of interior bodies sorevealed are amazing to look at, revealing a great deal about theinternal structures without invasive surgery. However, as far as thephysics of the x-ray interaction with the specimen, these tomographicreconstructions represent nothing more than an elaborate map of x-rayabsorption—a sophisticated shadowgraph.

Over time, other imaging tools for x-ray optical systems were invented.An apparatus using grazing incidence reflection from surfaces providedcone reflectors [C. G. Wang, U.S. Pat. No. 4,317,036] and capillarycollimators [F. Kumasaka et al., U.S. Pat. No. 5,276,724] to allow adiverging x-ray beam to be manipulated into a collimated beam or toconcentrate x-rays onto a specimen.

Systems using an x-ray microscope for the inspection of integratedcircuits have been disclosed by the Xradia Corporation [W. Yun and Y.Wang, U.S. Pat. No. 7,119,953; Y. Wang et al., U.S. Pat. No. 7,394,890;M. Bajura et al., U.S. Pat. No. 8,139,846; <http://www.xradia.com/>].FIG. 1 illustrates a prior art x-ray microscope system as disclosed onDrawing Sheet 2 of U.S. Pat. No. 7,119,953. In such a system, x-raysfrom a source 010 are collected by a condenser 012, which relays x-raysfrom the source 010 to a test object 020 to be examined. This condenser012 is described in some embodiments as a capillary condenser with asuitably configured reflecting surface, while in others as a zone plate.The converging beam from the condenser 012 irradiates the test object020 to be examined, and the radiation emerging from the test object 020to be examined is scattered and diffracted out of the path of the directradiation beam. An x-ray objective 041 is therefore used to form animage of the object, collecting the scattered x-rays. This objective 041is described as being possibly a zone plate lens, a Wolter optic, or aFresnel optic. In some embodiments, an additional phase plate 045, oftenin the form of a ring around the center axis of the system, is includedto enhance contrast. Both the phase plate 045 and the objective 041 aredescribed as being attached to a “high-transmissive substrate” 048 toform a composite optic 040. The focused radiation 051 forms an image ofthe test object 020 on a detector 050, which is described as possiblycomprising in some embodiments a charge-coupled device (CCD), and insome embodiments comprising a scintillator, and in others being afilm-based detector.

X-ray systems with Fresnel zone plate (FZP) optics such as this priorart Xradia system can be effective for the non-destructive examinationof integrated circuits, but the limitations of the zone plate optics [J.Kirz and D. Attwood, “Zone Plates”, Sec. 4.4 of the “X-ray DataBooklet”<http://xdb.lbl.gov/Section4/Sec_4-4.html>] reduce thewavelength range over which x-rays can be effectively collected, therebydecreasing the collection efficiency and increasing the time to collectdata for a complete IC. The system is therefore very slow andinefficient for collecting large volumes of data on multiple layers ofan IC.

X-ray systems using point projection microscopy (PPM) provide anotherway to form images of ICs, PCBs, or other packaging structures such asinterposers. These systems form direct shadows of objects using x-raysemitted from a small point source. Such a prior art x-ray inspectionsystem is the XD7600NT manufactured by Nordson DAGE of Aylesbury,Buckinghamshire UK.

A schematic of a PPM system is illustrated in FIG. 2. In a PPM system, a“point” source 10 emits x-rays 11 at a wide range of angles. The object20 to be examined comprising detailed structures 21 is placed somedistance away, so that it casts an enlarged shadow 30 comprisingfeatures 31 corresponding to the structures 21 on a detection screen 50some distance behind the object.

The advantage to such a system is its simplicity—it is a simple shadowprojection, and the magnification can be increased by simply placing thedetector farther away. By not using inefficient zone plates, higherintensity and therefore faster image collection times are achieved.

For an object of infinite thinness and with no internal structure, thismay be adequate. Unfortunately, ICs and packaging materials are notinfinitely thin; they have complex 3D structures, and the wide angularrange of the shadow projection system means that identical featuresilluminated at an angle cast very different shadows from those samefeatures illuminated head on. This parallax error, illustrated in FIG.2, must be taken into account in the image analysis of any shadowprojection system, and prevents its easy use in an inspection system,since pixel-by-pixel comparison is impossible for images taken withdifferent illumination angles.

Resolution is also an issue with PPM systems. Although x-ray wavelengthscan be chosen to be short enough that significant diffraction does notoccur, blurring is still a significant problem. The “point” source isactually the spot where an electron beam collides with an anode, and atypical x-ray source spot is at least 1 micron in diameter. Theresolution of the shadow is therefore limited by the size of theoriginal source spot, and at some distance, the shadows from an extendedsource will blur.

This blurring is illustrated in FIG. 3. For an object 20 with an opaquefeature 21 of width A, a “point” source 10 of size S a distance L₁ awayfrom the object 20 casts a shadow 31 of width A₁ corresponding to theopaque feature 21. At the edge of the shadow 31, the extended source 10also casts an extended penumbra 32 of width A₂. The larger the extendedsource 10, the larger the penumbra 32, and the poorer the image contrastand resolution. [Note: a penumbra will appear on all sides of theshadow; only one is shown for illustrative purposes. It should also benoted that the penumbra for a PPM system will not be symmetric foroff-axis features due to the parallax effects illustrated in FIG. 2.]

Throughput is therefore also an issue with PPM systems. To achieve thenecessary resolution, all the x-rays must be emitted from as small apoint as possible. Because x-rays are usually generated by colliding abeam of electrons into the surface of a metal, and there are thereforelimits on the brightness that can be achieved from a single spot.Attempts to increase the current too high will not increase thebrightness from the point source, but instead may simply melt the a holein the anode. Attempts to increase the x-ray flux by extending the areaof the source spot reduce the system resolution further. The x-raytarget must generally be a thin foil, to limit the size of the x-rayspot due to electron scattering in the target. As a rule of thumb,approximately 1 watt of electron-beam energy can be deposited into a 1micron spot on this type of x-ray target. Better resolution can only beobtained by reducing the size of the electron beam generating thex-rays, which in turn requires the beam current to be reduced to avoidthermal damage to the thin target. No existing x-ray source with spotsize of 1 micron has been able to reliably operate at over 10 watts ofpower.

Therefore, existing x-ray systems lack sufficient resolution and imagingspeed to meet the needs for high-resolution, high-throughput IC andelectronic packaging inspection. Therefore, a new approach is needed tocombine the penetrating power of x-rays with high-power,high-resolution, telecentric imaging techniques to provide measurementand inspection capabilities for the next generation of 3D and 2.5Dintegrated circuit packages, such as silicon interposers with TSVs.

BRIEF SUMMARY OF THE INVENTION

The inventions disclosed herewith comprise an x-ray system and variousmethods using an x-ray system. The x-ray system uses proximity imagingwith a high-resolution scintillator coupled to a camera. The object tobe examined is mounted in close proximity to a thin scintillator thatconverts x-rays into visible light. When collimated x-rays are directedat the object, a detailed high-resolution close proximity x-ray shadowimage is created on the scintillator. The thin scintillator convertsthis x-ray shadow image into a high-resolution visible light image, anda high-magnification optical microscope creates a magnified opticalimage of the scintillator on a 2D optical sensor, such as acharge-coupled device (CCD) or complementary metal-oxide-semiconductor(CMOS) detector.

One advantage of the x-ray system architecture disclosed herewith is anincrease in the x-ray flux. The system architecture can be implementedusing embodiments that allow the full spectrum of x-rays, or asubstantial portion thereof (e.g. greater than 1 percent of the energyspread of the beam) to be used for image formation, and that furtherallow the ratio of the x-ray source spot size to the resolution of theimaging system to be greater than 1 while simultaneously achieving ahigh contrast image resolution smaller than 10 microns (and in somecases, achieving sub-micron resolution).

The detector is coupled to electronics that convert the image toelectronic signals. The resulting electronic representation of the 2Dimage of the object is stored in computer memory by the electronics.

This electronic image from the x-ray system can then be used formetrology, in which the contents and structure of the image are analyzedto determine information about the physical dimensions of the object.Measurements can also be made within the image or between features inmultiple aligned images to detect variation in the materials andmanufacturing processes used.

Multiple images of the same object made using different angles ofincidence can also be used to determine 3-dimensional structures withinthe object. Because the x-rays can penetrate multiple layers of thestructure, the structures can be determined without disassembling theobject.

This electronic image from the x-ray system can also be used forinspection, in which the dimensions of the object determined from theimage are compared with a set of rules, or in which the image of theobject is compared with other images used as a reference to determine ifthere is a defective structure within the image. Defect detection andlocation identification can occur manually, or by comparison with otherareas within the object, or by comparison with stored information suchas an image of a similar device known to be correctly manufactured.

The use of images and measurements obtained from the x-ray system duringthe development and manufacture of components, such as those utilizingemerging interconnect technologies such as 2.5D IC, 3D IC, fine pitchTSVs, flip chip microbumps, interposers, etc., can accelerate processdevelopment and time to market for these new technologies.

The present invention addresses the need for a rapid, real time or nearreal time inspection tool for fine pitch detail including TSV, flip chipand interposer applications as well as any rapid inspection of MCPdevices. The present invention may be used in a failure analysis lab, orinline with the TSV or MCP packaging processing. The rapid real time ornear real time advantages of the invention allow feedback during theMCP, interposer or TSV packaging, manufacture or processing and allowsignificant yield improvement. Other advantages allow real timealignment of interposers and TSV dice.

The electronic image or images from the x-ray system can also be usedfor manufacturing process quality control or failure analysis, in whichdefects are detected by an inspection system using the x-ray images, andthe defect information is used in determining the origin of the defects.

The electronic image or images from the x-ray system can also be usedfor yield improvement, in which the origin of defects detected by aquality control or failure analysis system using the x-ray images isused in identifying and eliminating the cause of the defects, improvingyield. This may be accomplished using the methods of statistical processcontrol (SPC).

In the absence of suitable tools for making these kinds of images andmeasurements at the pitches and dimensions required by new generationsof manufacturing technologies, the economic feasibility of thesetechnologies and the potential digital products that use them will beimpacted negatively through higher cost and poor yields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art x-ray microscope system from the XradiaCorporation as disclosed in U.S. Pat. No. 7,119,953.

FIG. 2 illustrates a prior art system for point projection microscopy(PPM).

FIG. 3 illustrates resolution and blur in a prior art system for pointprojection microscopy (PPM).

FIG. 4 illustrates an overview in cross-section of an embodiment of anx-ray imaging system according to the invention.

FIG. 5 illustrates the system of FIG. 4 in more detail.

FIG. 6 illustrates in more detail the image formation elements thesystem of FIGS. 4 and 5.

FIG. 7A presents an image of a test pattern collected using a prior artPPM x-ray system.

FIG. 7B presents an image of the same test pattern used in FIG. 7A,collected using an x-ray system according to the invention.

FIG. 8A presents an image of the high-resolution features of a testpattern collected using a prior art PPM x-ray system.

FIG. 8B presents an image of the high-resolution features of the sametest pattern used in FIG. 8A, collected using an x-ray system accordingto the invention.

FIG. 9 illustrates an embodiment of the invention in which the x-raysource can be moved.

FIG. 10 illustrates an aperture being used to shape a beam as used insome embodiments of the invention.

FIG. 11 illustrates an embodiment in which the support for the objectbeing examined is provided by a membrane.

FIG. 12A illustrates one embodiment of a membrane support having acircular aperture.

FIG. 12B illustrates a cross-section view of the membrane support ofFIG. 12A.

FIG. 13A illustrates one embodiment of a membrane support havingfinger-like structures.

FIG. 13B illustrates a cross-section view of the membrane support ofFIG. 13A.

FIG. 14A illustrates one embodiment of a membrane support havingfinger-like structures and a thin film overcoat.

FIG. 14B illustrates a cross-section view of the membrane support ofFIG. 14A.

FIG. 15 illustrates an embodiment in which the object being examined andits membrane support are tilted.

FIG. 16 illustrates an embodiment in which the object being examined andthe scintillator assembly are supported by a membrane.

FIG. 17 illustrates an embodiment in which the object being examined,the scintillator assembly, and its membrane support are tilted.

FIG. 18 illustrates an overview in cross-section of an embodiment of anx-ray imaging system according to the invention in which the objectbeing examined and the detector for the image are both tilted.

FIG. 19 illustrates an overview in cross-section of an embodiment of anx-ray imaging system according to the invention a fiber-optic bundle isused to convey the image to the detector.

FIG. 20 illustrates the emission of light from a tilted scintillator.

FIG. 21 illustrates an embodiment of the invention using a prism.

FIG. 22A illustrates scattering of scintillator emission from a dustparticle when no coating is used on the scintillator.

FIG. 22B illustrates scattering of scintillator emission from a dustparticle when an attenuating coating is used on the scintillatoraccording to the invention.

FIG. 22C illustrates scattering of scintillator emission from a dustparticle when a reflective coating is used on the scintillator accordingto the invention.

FIG. 23 illustrates an embodiment of the invention in which thescintillator is attached to the optical system.

FIG. 24 illustrates a cross-section overview for a system additionallycomprising control systems for the optical system.

FIG. 25 illustrates a block diagram of a computer system as usedaccording to the invention.

FIG. 26 illustrates a typical process flow for making a metrologymeasurement using the x-ray system according to the invention.

FIG. 27 illustrates a typical process flow for using metrologymeasurements gathered according to the process flow of FIG. 26 formanufacturing process control.

FIG. 28 illustrates a typical process flow for carrying out inspectionusing the x-ray system according to the invention.

FIG. 29 illustrates a typical process flow for using inspection resultsgathered according to the process flow of FIG. 28 for yield managementin a manufacturing process.

FIG. 30 illustrates an example of resolution and blur in a systemaccording to the invention.

Note: Elements shown in the drawings are meant to illustrate thefunctioning of the invention, and have not been drawn to scale.

DETAILED DESCRIPTIONS OF EMBODIMENTS OF THE INVENTION Embodiments of theInvention

The system and methods disclosed in this Application all comprise asystem or the use of a system that illuminates an object to be examinedor inspected with x-rays, converts x-rays to visible (or near-visible)photons, forms an image of the visible (or near-visible) photons, andthen converts the image into an electronic form.

As such, the various embodiments of this x-ray image formation systemwill be presented first, followed by the various embodiments of methodsand systems that utilize the x-ray imaging system.

Although many kinds of objects can be examined or inspected using theapparatus disclosed here, it is expected to be especially suitable forthe examination and inspection of integrated circuit wafers andpackaging assemblies. One example of these are silicon interposers,comprising silicon with multiple TSVs, but the invention can also beused for the inspection of an integrated circuit (IC) itself, a siliconinterposer, a silicon dioxide interposer, a printed circuit board (PCB)with or without ICs already installed, a 3D IC package or assembly, a2.5D IC package or assembly, a multi-chip module (MCM), asystem-in-package (SIP) and other electronic microdevices or portionthereof that comprise microscopic structures. These may be examined asincoming materials, completed products, or as partially manufacturedobjects at any stage of their manufacture for the purpose of metrology,process control, inspection, or yield management.

Non-electronic devices with micro- or nano-structures, such as magneticrecording media, photonic structures and photonic crystals,metamaterials, etc, can also be examined and inspected using thisinvention. Capacitive sensors, such as fingerprint sensors, can also beexamined. A particularly attractive feature of the apparatus is that itis possible to make non-destructive, high-resolution observations andmeasurements of features within an object that cannot otherwise be seenusing electrons or optical photons, as are used in conventionalmetrology and inspection tools.

In general, objects suitable for use with this invention will compriseat least one flat side. Examples include: electronic circuits onsemiconductor wafers, parts of wafers or selected areas on wafers;integrated circuit chips, dice, assemblies, packages, or portionsthereof; micro-fluidic devices; micro-electro-mechanical systems (MEMS),including accelerometers, gyros, magnetic and capacitive sensors and thelike; photonic devices, particularly those fabricated using planarwaveguides; biological tissues, including stained samples; photomasks ortemplates for printing or fabricating any of the above mentioneddevices; and solar cells, parts thereof or parts pertaining to solarcells. Other objects without flat sides may be observed and inspected aswell, but the image quality may not be uniform for objects of irregulardimensions.

X-Ray Imaging System.

FIGS. 4 through 21 illustrate various embodiments of an x-ray imagingsystem according to the invention. Those skilled in the art will realizethat these illustrations each depict only one possible embodiment, andthat the figures illustrate the relative placement of elements. Theactual items as depicted are not intended to be interpreted as beingdrawn to scale with respect to each other, nor is the verticalorientation as depicted in some figures intended to be limiting—thearrangement of elements can be oriented in any manner, includinghorizontally on a table, or even inverted, with a source below and thedetector above.

FIG. 4 illustrates an overview of an embodiment of an x-ray imagingsystem according to the invention. An x-ray emitter 101 emits x-rays111. These x-rays are then shaped into a collimated x-ray beam 211, insome embodiments using distance from the emitter 101 and a plate 140with an aperture 142. This collimated x-ray beam 211 then illuminates anobject 200 to be examined. The x-rays that are transmitted through theobject 200 illuminate a scintillator assembly 300 comprising ascintillator 310 and, in some embodiments, a support 350 for thescintillator. The scintillator 310 absorbs a portion of the x-rays andreleases some of the energy so absorbed with the emission of visiblephotons 411.

Using an optical system 400, a magnified image 511 of the visiblephotons 411 emitted by the scintillator is formed on an image detector500. The image detector 500 converts the intensity of the magnifiedimage 511 to an electronic signal. The image detector 500 can comprisean electronic sensor, such as a charge-coupled device (CCD), or anotherimage sensor known to those skilled in the art. The electronic signal istransmitted to a system of electronics 600 that, in some embodiments candisplay the image results, and in some embodiments can store the imageresults and/or perform image processing algorithms on the image resultsin conjunction with a computer system 700.

For any source emitting ionizing radiation such as x-rays, it is oftenwise to provide shielding 998 around the x-ray source 100, and in somesituations legally required for operation. Such shielding 998 can be asimple enclosure of shaped sheets of lead metal, or a more intricatedesign fabricated from any of a number of x-ray absorbing materials,such as lead-doped glass or plastic, that will be known to those skilledin the art. Shielding is desirable to keep random x-rays, eitherdirectly from the emitter 101 or reflected from some other surface, fromcausing unwanted effects, particularly spurious signals in the variouselectronic components used to control the system.

Likewise, for some embodiments, additional shielding 999 around the beampath may also be desired, and in some cases be legally required foroperation. Such additional shielding 999 can be a simple enclosure ofshaped sheets of lead metal, or a more intricate design fabricated fromany of a number of x-ray absorbing materials such as lead-doped glass orplastic, that will be known to those skilled in the art. Additionalshielding 999 is desirable to keep random x-rays, either directly fromthe emitter 101 or reflected from some other surface, from causingunwanted effects, particularly spurious signals in the variouselectronic components used to control the system.

Because certain image detectors 500 such as those comprising CCD sensorscan be particularly sensitive to x-ray exposure, in some embodiments aportion of the scintillator assembly 300 can also be fabricated in wholeor in part using a material, such as a lead-doped glass, which absorbsx-rays while transmitting the visible photons 411 emitted by thescintillator. Other embodiments comprising a system design that placesthe image sensor 510 out of the x-ray beam path, as will be disclosed inmore detail later in this Application, may also be used if additionalisolation from x-rays is desired.

FIG. 5 shows the embodiment of the x-ray system of FIG. 4 in moredetail. Some elements, such as the additional shielding 999, may stillbe used in conjunction with this embodiment, but are not shown in FIG. 5to allow other additional details to be shown with more clarity.

In FIG. 5, an x-ray source 100 comprises an x-ray emitter 101 that emitsx-rays 111. One technique to generate x-rays is to accelerate a beam ofelectrons with high voltage and collide the electrons into an anodetarget fabricated from a designated material. In the embodiment shown, ahigh voltage is created by a power supply 119 and connected throughpositive lead 114 and negative lead 112 to create a high voltage betweenan electron source 102 and an anode 104, which serves as the x-rayemitter 101. Electrons 103 are then emitted from the electron source 102to collide with the anode 104, creating x-rays 111.

A window 115 in the x-ray source 100 may be provided if maintaining avacuum or having a fill gas of some particular composition and/orpressure in the x-ray source 100 is desired. The window 115 may compriseberyllium or some other x-ray transparent material.

The energy of the x-rays 111 emitted for such an x-ray source 100 willtypically vary depending on the spot size, the accelerating voltage, theelectron current, and the target materials of the emitter 101. Theseparameters can be adjusted and optimized independently or together togenerate x-rays with particular properties. For one embodiment for anx-ray source 100 in a system designed to examine copper (Cu)micro-structures, the spot size of the emitter 101 is 1 millimeter indiameter, the accelerating voltage for electrons is 75 kV, the currentis 20 mA, and the target anode is fabricated from tungsten (W). Thisproduces x-rays of with an energy of 20-30 keV (corresponding to awavelength range of 0.062-0.041 nanometers). If lower energy x-rays(e.g. 1.7 keV, corresponding to a wavelength of 0.730 nanometers) aredesired for examining structures fabricated from aluminum (Al), anaccelerating voltage of 5-10 kV can be used with a target anodecomprising silicon (Si) or silicon compounds. In some embodiments, anaccelerating voltage between 90 and 160 kV can be used. The choice ofwindow material and thickness will affect the low-energy range of thex-rays due to x-ray absorption.

One example of an x-ray source is the MXR-75HP/20 1 kW x-ray sourcemanufactured by COMET Industrial X-ray of Flamatt, Switzerland. In otherembodiments, the x-ray source 100 can be a fixed or rotating anode x-raytube, a synchrotron, a liquid metal source, or any other x-ray sourceknown to those skilled in the art. The x-ray source may be operated in acontinuous mode or a pulsed mode. Other specific x-ray sources orsynchrotron sources will be known to those skilled in the art.

X-rays 111 from an emitter 101 generally emit in all directions.However, for high-resolution imaging, collimated x-rays are oftenpreferred. Illumination of an object 200 to be examined with collimatedx-rays can be achieved either by providing enough distance between theemitter 101 and the object 200 to be examined, so the angular spread ofthe x-ray illumination at the object 200 is small, or by using a varietyof x-ray beam shaping optical elements such as zone plates or x-raymirrors. In one embodiment, using a 1 kW x-ray source with a source spotsize diameter of 1 mm and no additional beam shaping elements toilluminate an object 200 with dimensions 1 cm×1 cm, with a separationdistance of 10 cm between the emitter 101 and the object 200, achieves abeam angular spread of about 1 milliradian at each point on the object200.

In some embodiments of the invention, one or more beam adjusters 125such as filters can be inserted between the emitter 101 and the object200 and used to change the x-ray energy spectrum in order to providebetter contrast, depending on the material composition of the object 200under examination. For example, if the object 200 contains copper (Cu)structures (e.g. copper TSVs) embedded in a material such as silicon(Si), the x-ray spectrum can be adjusted to increase the relativeportion of the x-rays with energy greater than the copper absorptionk-edge at 8.9 keV. This can be achieved by increasing the electron beamvoltage generating the x-rays, which increases the portion of the x-rayspectrum that is more energetic, or by using a beam adjuster 125comprising, for example, aluminum (Al) metal to absorb lower-energyx-rays. This can lead to an adjusted x-ray beam 211 with energy that ispeaked near 8.9 keV, thus increasing the contrast of the copper relativeto the silicon substrate.

In some embodiments, the window 115 of the x-ray source may be selectedto also function as a metallic filter, eliminating any need for aseparate element such as a beam adjuster 125 to serve this function. Insome embodiments, the beam adjuster 125 can also comprise beam shapingoptics, such as capillary collimators, grazing incidence reflectingcones, zone plates, crystals and the like to further shape the x-raybeam angle and direction, as well as the energy spectrum. In someembodiments, an x-ray monochromator may also be inserted between thex-ray emitter 101 and the object 200 and be used to select a specificx-ray beam energy.

Aside from beam adjusters 125, the beam path between the emitter 101 andthe object 200 can also include one or more shutters 130 to limit thetime of x-ray exposure as well as a plate 140 with an aperture 142 tolimit the physical extent of the x-ray beam. The shutter 130 can beelectronically driven by a shutter controller 139 through a connector138 such as an electrical lead, which in turn can be synchronized withthe computer system 700 controlling the system, or can be operatedmanually by some other means. Mechanical alteration of the x-rayintensity (e.g. turning the x-rays on and off) can also be achieved insome embodiments by controlling the x-ray source power supply 119 usingthe controller 139.

The beam path between the window 115 of the x-ray source and the object200 in some embodiments will be filled with ambient air at standardconditions of temperature, pressure and/or humidity, but canalternatively be filled with a designated gas composition at varioustemperatures and pressures, or even pumped out to low pressure or to bea vacuum. This may be of more concern if the object 200 to be examinedwill be heated or cooled during the time the images are collected, andan environment without oxygen, for example, may help prevent corrosionor change in the object 200.

For such an embodiment, the system may be additionally provided with achamber 180 to contain the beam path and the appropriate portions of thex-ray source 100. This chamber 180 may be inside or outside theadditional shielding 999. This chamber 180 can be further connected toone or more sources of gas 182 with a suitable means, such as a gasvalve 183, for adding amounts of gas to the chamber. This chamber 180can additionally be connected to a vacuum pump 184 with a suitablemeans, such as a vacuum valve 185, for removing amounts of gas from thechamber. The gas composition and conditions can be selected based on theenergy of the x-rays and the environmental requirements of the object200 under examination. For example, if low energy x-rays are to be usedto provide better contrast for aluminum (Al) structures within anobject, such as the interconnect layers in traditional IC, filling thebeam path with helium may be preferred.

In some embodiments, the object 200 to be examined may be placed indirect contact with the scintillator 310. However, in other embodiments,the object 200 will be placed in a mount 250 and positioned in closeproximity to the scintillator. This mount 250 can be a clamp, a vise, astage (including a stage designed to hold manufactured silicon wafers),an air bearing, a membrane support, or any number of support structuresthat will be known or can be designed for observing objects of varioussizes, shapes and compositions.

The mount 250 in some embodiments will allow the object to be movedrelative the x-ray beam. Translation motion in x-y planes (with x- andy-axes defined as orthogonal axes in the plane of the scintillator) willallow observation of an object 200 larger than the size of the beam.Adjustment along the z-axis (i.e. along the direction perpendicular tothe scintillator) will allow the object 200 to be moved as close aspractical to the scintillator, improving resolution. Rotation in the x-yplane (around the z-axis) may also be used to align images of the objectwith axes of manufactured objects within the object (e.g. aligningcopper wires in the object to appear horizontal or vertical in theimage).

Tilting the object 200 by rotation of the mount 250 around the x- ory-axis can also allow observation of an object 200 using differentangles of incidence for the x-rays. Multiple images at multiple anglescan be used to allow the reconstruction of 3D structures that a singleimage may not provide. More information on these embodiments will beprovided later in this Application.

In some embodiments, the motion of the mount 250 is controlled by acontroller 259 through a connector 258. The controller 259 is in turndirected either by direct input from an operator, or by electronicinstructions provided by the computer system 700.

The adjusted x-ray beam 211 illuminates the object 200 to be inspectedas it is held in the mount 250. Depending on the nature and constructionof the object, it may comprise various internal 2D and 3D structures ofvarious material compositions. These various materials can have varyingdegrees of absorption for the adjusted x-ray beam 211, producingdifferent levels of transmission intensity. For example, for x-rays withan energy of 20 keV, absorption by 10 microns of silicon will be about1%, while that of 10 microns of copper will be about 26%.

Referring now to FIG. 6, which illustrates elements of the embodiment ofFIGS. 4 and 5 in more detail, the object 200 to be inspected isillustrated as a silicon interposer 200-I, comprising a silicon waferwhich can be, for example, 500 microns thick, with multiple copper TSVs210 fabricated in the wafer and extending from one face of the siliconwafer to the other. Copper TSVs typically have a cylindrical shape, andcan typically range from 1 to 150 microns in diameter and be fabricatedin a wide range of pitches, for example, from a pitch range of 20 to 500microns.

The variable transmission of x-rays through the silicon and copper ofthe TSVs 210 results in a pattern of intensity in the output x-rays 311emerging from the object 200-I, shown as the absence or presence ofcontinuing arrows in the figure. The output x-rays 311 propagate towardsthe scintillator assembly 300. The distance between the object 200-I andthe scintillator assembly 300 can be as large as 1 mm, but if thedistance between the object 200-I and the scintilltor assembly 300 issufficiently small, typically on the order of 100 microns or smaller,there will be little scattering or spreading of the output x-rays 311between the object and the scintillator, and the profile of the emittedvisible photons 411 from the scintillator will more accurately reproducethe intensity of the output x-rays 311. In some embodiments, betterpattern fidelity can be achieved if the propagation distance isminimized, and the object 200-I and the scintillator assembly 300 are inclose proximity. In some embodiments, the object 200-I being examinedmay actually be in direct contact with the scintillator assembly 300itself. More variations of these embodiments are disclosed later in thisApplication.

The scintillator 310 comprises a material designed to absorb x-rays andemit visible photons 411. Although many such materials are known tothose skilled in the art, one such material is lutetium aluminum garnet,doped for activation with cerium (LuAG:Ce, chemically represented byLu₃Al₅O₁₂:Ce), which emits green light at 535 nm when x-rays areabsorbed. LuAG:Ce is both mechanically and chemically stable, and itshigh density (6.76 g/cm³) and hardness (8.5 Mho) allows a thinnerscintillator screen (thinner than 50 microns) with higher emission to befabricated. Scintillator materials are generally grown as singlecrystals, and then polished to be thin crystal wafers that are bothoptically smooth and relatively thin.

Other scintillator materials are: lutetium aluminum garnet doped withpraseodymium (LuAG:Pr), yttrium aluminum garnet (YAG, Y₃Al₅O₁₂) dopedwith cerium or praseodymium (YAG:Ce, YAG:Pr), bismuth germanate (BGO,Bi₄Ge₃O₁₂), lutetium oxyorthosilicate (LSO, Lu₂SiO₅), gadolinium galliumgarnet doped with chromium (GGG:Cr, Gd₃Ga₅O_(i2):Cr), and sodium iodidedoped with thallium (NaI:Tl). Other scintillator materials, bothfabricated from crystals and from and organic compounds embedded inplastic, will be known to those skilled in the art. Commercialscintillator screens are available from companies such as Saint GobainCrystals of Hiram, Ohio.

Specific embodiments of the scintillator 310 can be designed to optimizeeither the emission brightness (which increases with scintillatorthickness) or the resolution of the emission pattern (which decreaseswith scintillator thickness, due to increasing emission blur). Otherembodiments can be co-optimized for both brightness and resolution. Insome embodiments, the scintillator 310 is a crystal of LuAG:Ce 1 cm indiameter and 20 microns thick. In other embodiments, the scintillator isa crystal of LuAG:Ce 1 cm in diameter and 5 microns thick.

In some embodiments, the scintillator 310 will be controlled forthickness and surface quality, minimizing thickness variations andsurface scratches. In some embodiments, the thickness variations will becontrolled to be less than 10%.

In some embodiments, the scintillator assembly 300 may simply comprise athin crystal of scintillator material. However, since such crystals canbe fragile and break if an object to be examined were to be placed incontact with the crystal with too much force, a scintillator withadditional mechanical supports and coatings may be preferred.

As illustrated in FIG. 6, in some embodiments the scintillator assembly300 may have a coating 320 on the side facing the x-ray source. Thiscoating 320 can prevent scratching of the scintillator 310 when theobject 200-I being inspected is placed in contact with the scintillatorassembly 300.

In some embodiments, as described in further detail below, the coating320 can be selected to have specific mechanical and optical propertiesthat reduce the impact of dust in the image.

In some embodiments, the scintillator 310 may also be attached to asupport 350 such as a substrate. The support 350 may be a glass slide 1mm thick made from conventional BK7 glass. This attachment of thescintillator 310 to the support 350 may be achieved by using anindex-matching adhesive between the scintillator and the substrate. Insome embodiments, the substrate can also provide shielding, transmittingthe visible photons 411 from the scintillator 310 to the optical system400 while also absorbing x-rays, so that unabsorbed x-rays transmittedthrough the scintillator 310 do not irradiate optical components, suchas an objective lens, which may be damaged by exposure to x-rays. Thiscan be achieved if the support 350 comprises a lead-doped glass. Onesuch glass comprising 65% lead oxide by weight is RD-50 radiationshielding glass manufactured by SCHOTT North America Inc. of Elmsford,N.Y.

Returning to FIG. 5, the emitted visible photons 411 are collected by anoptical system 400 that forms a magnified image 511 of the emittedvisible photons 411. The magnification of the optical system 400 can beas small as 1×, but more typically will be designed to magnify the imageby 10× to 100×.

In some embodiments, the optical system 400 comprises an objective lens410. This objective lens can be similar to those commonly used formicroscopy applications. In some embodiments, the objective lens will bea 10× lens, with a numerical aperture (NA) of 0.23. One such objectivelens is a Nikon Plan 10× objective lens, manufactured by the NikonCorporation of Tokyo, Japan. The objective lens 410 may also haveelements manufactured using radiation-hard glass, to reduce the effectsof x-ray radiation exposure on the optical components.

In some embodiments, the optical system 400 also comprises a transfer ortube lens 450 to relay the image from the objective lens 410 to theimage detector 500. The transfer or tube lens 450 may also serve toadditionally magnify the optical image. The transfer or tube lens 450may also have elements manufactured using radiation-hard glass, toreduce the effects of x-ray radiation exposure to on the opticalcomponents. The transfer or tube lens 450 may also have elementsmanufactured using lead-doped glass, to provide additional absorption ofx-rays and shielding for the optical sensors in the system.

In some embodiments, the optical system 400 can comprise additionalelements 425 in the optical path to alter properties of the opticalimage. These additional elements 425 can comprise neutral density (ND)filters to decrease the intensity of the light reaching the detector andotherwise shape and adapt the image. Conversely, additional elements 425can comprise an image intensifier to increase the intensity of lightreaching the detector. Additional elements 425 in the optical path mayalso comprise elements fabricated from lead-doped glass to furthershield the detector from x-rays.

Although the figures have illustrated the various optical components ofthe optical system 400 in a particular configuration, these can beassembled in a number of arrangements. Optical systems may or may notcomprise a tube lens, may or may not comprise a filter, etc. If a filteris used, the filter may be between the transfer or tube lens 450 and theimage detector 500, or may be integrated as a component within theobjective lens 410 or the transfer or tube lens 450. Other arrangementsand embodiments will be apparent to those skilled in the art.

An image detector 500 is used to detect the magnified image 511 of thevisible photons 411. In some embodiments, this image detector 500comprises an image sensor 510 such as a charge-coupled device (CCD) withassociated electronics 550. This image sensor 510 can be placed in theimage plane of the optical system 400 to convert the magnified image 511of the visible photons 411 emitted by the scintillator 310 intoelectronic signals.

A CCD Camera will have a number of image sensing elements, typicallyarranged in a square or a rectangular array. Each element can generate apixel of the electronic image, with the electronic signal comprisingdata representing the position of the pixel and the image intensity. Theposition of the pixel can be calibrated into x-y coordinates for thecorresponding position on the object 200 being examined.

One example of a camera with a CCD image sensor is the Prosilica GT 27506 Megapixel CCD camera for extreme environments, manufactured by AlliedVision Technologies. The camera uses an ICX694 EXview HAD CCD sensorwith 6.09 megapixels, capable of generating 25 frames/second,manufactured by Sony Corporation of Tokyo, Japan. When used with a 10×objective having an NA=0.23, a single CCD image pixel corresponds to0.453 microns, making this an x-ray imaging system with sub-micronresolution.

Although the frame rate from this camera can be 1/25 of a second, thelow light intensity emitted by the scintillator leads in someembodiments to using a longer integration time in the CCD sensor andelectronics. Typical single pixel integration time in the abovedescribed embodiment is 8 seconds.

Faster image generation speed at the cost of resolution can be achievedby “binning” the pixels, collecting the signals from several pixels intoone image pixel. In the above embodiment, when 8×8=64 sensor pixels arebinned into one image pixel, an image can be generated in 1 second. This“binning” mode can be especially useful for real-time navigation andalignment for specific structures within an object 200 to be examinedbefore a final, high-resolution image is collected. “Binning” can beaccomplished using 2×2, 4×4, 8×8, or other combinations of sensorpixels.

Faster image collection can also be achieved by using a greater x-rayflux, which in turn increases the number of photons emitted by thescintillator 310.

In other embodiments, the image sensor 510 may be a front-illuminatedCCD or a back-thinned CCD capable of detecting ultraviolet (UV) light.The CCD may be operated in interline-transfer mode, frame-transfer modeor as a time-delay and integration (TDI) sensor. The image sensor 510may also be a CMOS sensor, or a “scientific CMOS” (sCMOS) sensor. Thesensor may also be cooled to below room temperature. Other imagecollection sensors will be known to those skilled in the art.

The electronic signal from the image sensor 510 is then transmittedthrough a connector 558 to a system of electronics 600 that, in someembodiments can display the image results, and in some embodiments canstore the image results and/or perform image processing algorithms onthe image results in conjunction with a computer system 700. Whenproperly calibrated, the electronic signals correspond to thetransmitted x-ray intensity at corresponding locations in the object200.

In addition to providing image signals from the detector 500 to thesystem of electronics 600, connector 558 may also provide informationfrom the system of electronics 600 to the detector 500 to controlsettings of various elements of the detector. In some embodiments of theinvention, connector 558 may extend beyond the detector 500 and connectthe system of electronics 600 with the optical system 400 as well,controlling various aspects of the optical system 400 (such as focus,aperture settings etc.).

In some embodiments, the system of electronics may read in the imagesover an internet connection (via packets), or a serial bus (e.g. USB2.0). In some embodiments, the system of electronics 600 may comprise aframe-grabber board and connection, such as the Orion HD highperformance graphics and video capture board manufactured by MatroxElectronic Imaging of Quebec, Canada.

One or more computer systems 700 may be used to control various aspectsof the x-ray system, including: properties of the x-ray source 100,including the angle of the x-ray source 100; the x-ray source powersupply 119; the controller 139 directing shutters 130 or other beamconditioning or shaping equipment; and the controller 259 directing thestage 250 that manages the position and/or orientation of the object200. In some embodiments of the invention, additional controllers can beused to control: properties of the optical system 400, includingfocusing or magnification; the operation of the sensor; and thecollection of images from the image detector 500.

The computer system 700 can be any of a number of commercially availablecomputers, such as an HP ENVY DV7-7212nr Notebook PC, comprising anIntel® Core i7-3630QM Processor; a 2 GB GDDR5 NVIDIA® GeForce GT 650MGraphics capability; a 750 GB 7200 RPM hard drive; a memory modulecomprising 8 GB DDR3 1600 MHz RAM (2 DIMM); and a 17.3-inch diagonaldisplay (1920×1080) display. More detail on possible variations for thecomputer system will be presented later in this disclosure.

Results of the X-Ray Imaging System.

Shown in FIGS. 7 and 8 are x-ray images of a test pattern havingsub-micron test features fabricated in gold on silicon. The smallestline/space pitch for the innermost circle is 1 micron, comprising 500 nmlines with 500 nm spaces. For each example, one image is generated usinga system constructed according to the embodiments described above, andone image is generated using commercial x-ray microscope using the priorart PPM configuration as previously described.

FIG. 7 illustrates an example of the larger size of the field of viewfor the system according to the invention. The image for the field ofview for a prior art PPM system is shown in FIG. 7A, and the field ofview for the system according to the invention is shown in FIG. 7B. Bothimages were both collected using a resolution where one pixelcorresponds to 0.5 microns, and with comparable integration times.

The system according to the invention clearly demonstrates a field ofview of 1.375 mm×1.1 mm, or 1.51 mm². This is more than 50 times largerthan the field of view of 0.20 mm×0.15 mm, or 0.030 mm², for the PPMsystem with comparable image contrast and quality. A set of imagescovering an entire IC or chip package will therefore be collected ˜50times faster using the system according to the invention than for theprior art PPM system.

FIG. 8 illustrates an example of the higher resolution for the systemaccording to the invention. Using the same test pattern shown in FIGS.7A and 7B, an image showing the resolution of the prior art PPM systemis shown in FIG. 8A, and an image showing the resolution of the systemaccording to the invention is shown in FIG. 8B. Both images werecollected using a resolution where one pixel corresponds to 0.1 microns,and with comparable integration times.

The system according to the invention clearly demonstrates a resolutioncapability for the smallest line/space features in the test pattern,which are 500 nanometers wide, while the prior art PPM system onlyresolves features as small as 1.5 microns (3 times larger than thesystem according to the invention), and only shows a blur for the 500nanometer features.

Further Embodiments of the X-Ray Imaging System.

The previous section disclosed an overview of several embodiments of thex-ray imaging system. Those skilled in the art will know some variationsof the system that may offer additional advantages in certainsituations. What follow are more detailed descriptions of embodiments ofthe invention.

X-Ray Source Variations.

Some embodiments of the invention may comprise additional variations ofthe x-ray source 100.

Referring now to FIG. 9, in some embodiments, the x-ray source cancomprise a mount 106 that can move the position of the x-ray source 100relative to the object 200, thereby changing the angle of incidence ofthe x-ray beam on the object. The mount 106 can be designed to allow thex-ray source 100 to swing in the x-z plane, in the y-z plane, or anyother combination of axes. The source can also be moved along the z-axisto move the x-ray source 100 closer to the object 200. This may have theeffect of making the beam brighter, increasing signal strength, at thecost of having an x-ray beam that is less collimated, reducingresolution. This effect may be reduced or eliminated by reducing thespot size of the x-ray source.

Motion of the x-ray source 100 using the mount 106 can be controlled bythe computer system 700 several ways. In some embodiments, the sourcemount 106 may move the x-ray source 100 to a fixed location to allow animage to be captured. In some embodiments, the mount 106 can move thex-ray source 100 continuously as images are gathered, allowing thedynamic change of x-ray intensity as transmitted through the object 200to be recorded as a function of illumination angle. In some embodiments,the x-ray emitter 101 can be moved to at least 10 degrees off the normalincidence angle.

In some embodiments, further adjustment of the angle of incidence of thex-ray beam 211 on the object 200 can be achieved by coordinating themotion of the x-ray source 100 using the source mount 106 with themotion of the object 200 using the object mount 250. This coordinationcan be done manually or using the computer system 700.

In some embodiments, the shielding 998 will be designed to enclose thex-ray source 100 and the source mount 106. In other embodiments, theshielding 998 can be designed to only enclose the x-ray source, with themount 106 designed to move the shielding 998 as it moves the x-raysource 100.

In some embodiments of the invention, multiple x-ray sources may be usedto produce images with different angles of incidence. The x-ray sourcesmay be fixed in space or moveable, and may be operated sequentially orsimultaneously. They can be operated manually or controlled by one ormore computer systems 700.

Beam Path Element Variations.

Some embodiments of the invention may comprise additional variations ofthe elements in the x-ray beam path.

X-rays 111 produced by the emitter 101 propagate in all directions fromthe source spot. In some embodiments, free space propagation and asuitable choice of distance to the object 200 and scintillator assembly300 can provide collimated or near-collimated x-rays incident on theobject 200. In some embodiments, such as that shown in FIG. 10, a plate140 with an aperture 142 can be placed between the emitter 101 and theobject 200 to select a portion of the x-ray beam 211 to continuepropagation to the object 200.

The plate 140 can be fabricated from any number of materials that absorbx-rays. The most commonly used material is lead (Pb). Other radiationblocking materials such as steel or lead-doped glass or lead-dopedpolymers may be used in some embodiments. Other radiation shieldingmaterials will be known to those skilled in the art. In someembodiments, the plate 140 may be attached to, or otherwise connectedwith the shielding 998 around the x-ray source 100 or the additionalshielding 999 around the beam path.

In some embodiments, the aperture 142 can be circular. In someembodiments, the aperture shape can be a square, rectangle, triangle,pentagon, trapezoid, or any one of a number of geometric shapes. Theaperture 142 can have a shape and size selected to be either the same orsimilar to the size and shape of the scintillator 310 or the object 200.The aperture 142 can be fabricated by simply punching a holeperpendicularly through the plate 140, or by the creation of moredetailed geometric shape, having, for example, edges beveled with aparticular angle.

Various dimensions for the thickness of the plate 140 can be used, withthe thickness being specified by a desired absorption for the x-rays.

In some embodiments, beam adjusters such as an x-ray filter may also beattached to the plate 140.

In some embodiments, the shutter may also comprise a plate with aperturethat allow transmission of an x-ray beam with particular shape andproperties.

In some embodiments, the shutter may also comprise both a filter and aplate with aperture that allow transmission of an x-ray beam withparticular energy spectrum as well as a particular shape and properties.

Mounting System Variations.

Some embodiments of the invention may comprise additional variations ofthe elements of the mount 250.

In some embodiments, the object 200 to be examined may be held by amount 250 that secures the object from the sides. In some embodiments,mount 250 may comprise a clamp or a vise. In some embodiments, theobject 200 to be examined may be held by a mount 250 that secures theobject from the sides and/or the edges. In some embodiments, the object200 to be examined may be held by a mount 250 that comprises an apertureso that the face of the object 200 facing the scintillator 310 isexposed. These various embodiments can allow the portion of the object200 facing the scintillator 310 to have nothing intervening in the spacebetween the object 200 and the scintillator assembly 300. In thesevarious embodiments, the mount 250 securing the object 200 may be movedto place the object 200 in very close proximity or in direct contactwith the scintillator assembly 300.

Referring now to FIG. 11 through FIG. 14, in some embodiments, such asthat illustrated in FIG. 11, the mount is a structure 250-M thatcomprises a membrane 254 that supports the object (now shown as aninterposer 200-I) to be examined. The membrane 254 with object 200-I canbe moved to be in close proximity or in actual contact with thescintillator assembly 300. In some embodiments, the membrane 254 may beopaque, to prevent light from the scintillator 310 from reflecting offthe object 200-I and scattering back into the optical system 400.

In some embodiments, the membrane 254 may be manufactured from aradiation resistant material such as Kapton®, a radiation resistantpolyimide film with mechanical and thermal stability having hightransparency for x-rays and insensitivity to radiation damage. Kapton®is a commonly used material for windows of all kinds in x-ray sources(synchrotron beam-lines and x-ray tubes) and x-ray detectors. A typicalcommercial Kapton® film is 25 microns thick, with thin Teflon® coatings2.5 microns thick on each side. Kapton® is manufactured by the E. I. duPont de Nemours and Company of Wilmington, Del.

In some embodiments, the membrane 254 may be comprise a carbon fiberfilm, such as Scotchprint® Wrap Film Series 1080™ vinyl filmmanufactured by the 3M™ Corporation of St. Paul, Minn.

In some embodiments, the membrane 254 may comprise beryllium, a rigidmetal with high transparency for x-rays as well as a high thermalconductivity and a low coefficient of thermal expansion.

In some embodiments, the membrane 254 may comprise glass or fusedsilica. In some embodiments, the membrane 254 may comprise a crystalsuch as quartz, LuAG, or other crystals listed above that are used forscintillators but without the doping that causes scintillation to occur.In some embodiments, the membrane 254 may additionally comprise anaperture, such that the membrane 254 supports the object 200, but theaperture allows the face of the object 200 being examined to be directlyexposed to the scintillator 310.

The mount 250-M comprising membrane 254 may also comprise supportstructures for the membrane 254. In some embodiments, as illustrated inFIG. 12A and FIG. 12B, these support structures 251 comprise aring-shaped object with an aperture in the middle, allowing the membrane254 to support the object 200 in the aperture. In some embodiments, asillustrated in FIG. 13A and FIG. 13B, these support structures 252comprise a pair of finger-like supports for the membrane 254. Otherdesigns and shapes for the support structures will be known to thoseskilled in the art.

In some embodiments, as illustrated in FIG. 14A and FIG. 14B, the object200 to be examined will have an additional overcoat 256 to secure it inplace. This overcoat 256 may also be a film made of Kapton®, carbonfiber, or other x-ray transparent materials known to those skilled inthe art.

In some embodiments, motion of the mount 250-M with support structures252, including translations in the x-y plane to change the position ofthe object 200, as well as vertical translations along the z-axis tomove the object closer to (or even in contact with) the scintillatorassembly 300, or further away from the scintillator assembly 300 (forexample, for loading or unloading the object 200), is also possible. Insome embodiments, rotation of the mount 250-M around various axes isachieved. In some embodiments, these various motions can be controlledby the same controller 259 as discussed above. In other embodiments,motion may be controlled by independent controllers.

Referring again to the embodiment of FIG. 11, the object 200-I moves butthe scintillator 310 does not; instead, the mount 250-M with membrane254 moves the object 200-I to allow images to be collected for differentlocations of the object. Another motion, perpendicular to the plane ofthe object 200-I, may also be actuated to cause the object 200-I and/ormembrane 254 to be brought into proximity or contact with thescintillator 310, or conversely moved away from the scintillator 310 forchanging objects or replacement of the membrane 254. In someembodiments, the object is attached to, or sits on, a membrane thatseparates the object from the scintillator. In this embodiment, themembrane may be opaque, to prevent light from the scintillator fromreflecting from the object into the optical system. The membrane may bemade from radiation-resistant materials, such as Kapton® or carbon fiberfilms. The membrane may serve as a stage to move the object over thescintillator, to permit viewing of different parts of the object.

In some embodiments of the invention, such as when the entire object 200to be examined is relatively small and can be imaged completely on theimage detector 500, the mount 250 can be a static mount that does notmove relative to the scintillator assembly 300 and the optical system400. In some embodiments, the mount 250 can be clamped or otherwiseattached to the scintillator assembly 300 to prevent relative motion orvibration. In some embodiments, the mount 250 can comprise an airbearing to support the object 200 under examination, which can provideboth close proximity for the object and the scintillator as well asuniform separation.

In some embodiments of the invention, such as when the object 200 to beexamined is large, and cannot be completely imaged entirely with theimage detector 500 in one exposure, the mount 250 for the object 200 cancomprise a motion control stage, which moves the object 200 in the x-yplane. In some such embodiments, an image can be collected for oneportion of the object 200 while it is static in one position, and thenthe object can be moved and stopped at a second position, and a secondimage can be collected for a second portion of the object. This processcan proceed until images from multiple areas or even the entire object200 have been collected.

In other embodiments, mount 250 can be designed so that the object 200to be examined moves continuously as x-ray exposures are made, and themotion only stops after images have been collected for a designatedportion or the entirety of the object 200. In such an embodiment, thex-ray source 100 may be operated in a pulsed mode to reduce the effectmotion will have on the blur in the resulting images. The pulsing can beachieved either by varying a voltage in the power supply 119 for thex-ray source 100, or by using the shutter 130 in the x-ray beam 211 tocontrol the exposure time. In some embodiments of the invention, themotion of the object 200 and the pulsing of the x-ray beam 211 can besynchronized, so that a stroboscopic effect is achieved. This can beespecially useful if the object contains periodic arrays, and the objectmoves by one period (or multiple thereof) between each pulsed exposure.The strobe effect may be used to limit blurring of an image withoutstopping the stage completely at each location an image is desired.

In some embodiments, the mount 250 comprises a wafer stage to support anentire silicon wafer. Typical silicon wafers used in manufacturing havediameters of 6 inches, 8 inches (200 mm), 12 inches (300 mm), and 450mm. Silicon wafer thicknesses typically vary with wafer diameter, with200 mm wafers having a thickness of 725 microns, 300 mm wafers having athickness of 775 microns, and 450 mm wafers having a proposed standardthickness of 925 microns. The electronic devices are typicallymanufactured on one side of the wafer, so for examination in the x-raysystem, if the object 200 to be examined is a silicon wafer, the waferwill be inverted to allow the side with the electronic devices to befacing the scintillator 310. In some embodiments, the wafer stage willcomprise a mounting system that holds the wafer by its edges, so thatthe x-rays are not attenuated by the wafer mount as they enter the rearof the wafer. One example of a wafer stage is the Razor™ AtmosphericTransfer Robot from Brooks Automation of Chelmsford, Mass.

In some embodiments of the invention, as was illustrated in FIG. 9, theangle of incidence of the x-rays on the object will be variable, and thesystem can be adjusted to take multiple images of the object to beexamined at multiple angles. When a set of images at pre-determinedangles are collected, the set of images can be used by a computerprogram to synthesize a 3D representation of the layers of the object.In some embodiments, this 3D synthesis can be achieved using thealgorithms of computed laminography (CL). These algorithms can beoperated on the one of more computer systems 700 controlling the system,or the images can be exported through a network to a different computerfor further analysis.

Referring now to FIG. 15, the angle of incidence for the x-ray beam 211on the object 200-I can also be adjusted by tilting or rotating theobject 200-I and mount 250-M.

Referring now to FIG. 16, in other embodiments the invention, the object200-I to be examined is placed in contact with the scintillator assembly300. In this embodiment, the entire scintillator assembly 300 is alsosupported by a scintillator mount 350-M, which can also comprises amembrane 354 and finger-like support structures 352 analogous to themount 250-M with membrane 254 and support structure 252 shown in FIGS.11, 13 and 14. In some embodiments, the scintillator mount may also beconstructed to comprise a support such as a thick substrate in place ofa membrane 354 to support the object being examined. In someembodiments, the membrane 354 may be selected to have properties similarto that of the earlier described support 350, such as stiffness,rigidity, and opacity to x-rays.

For the embodiment shown in FIG. 16, the membrane 354 is now between thescintillator 310 and the optical system. In this case, the opticalsystem must be designed to anticipate this additional optical elementaffecting light from the scintillator, and will therefore be a modifiedoptical system 400-M and may not be identical to the earlier describedoptical system 400.

Additional embodiments of the invention may comprise a membrane 354 tosupport the scintillator assembly as previously described for the mount250 for the object 200. In some embodiments, the membrane 354 maycomprise Kapton®, glass or fused silica, a crystal such as quartz, LuAG,or other crystals listed above that are used for scintillators butwithout the doping that causes scintillation to occur. Other materialsthat are transparent to visible photons that can be used for membranesmay be known to those skilled in the art.

In some embodiments, the mount 350 may secure the scintillator assembly300 from the sides. In some embodiments, mount 350 may comprise a clampor a vise. In some embodiments, the mount 350 may secure thescintillator assembly 300 from the sides and/or the edges. In someembodiments, the mount 350 that secures the scintillator assembly 300may comprise an aperture so that the face of the scintillator assembly300 facing the optical system 400 is exposed. These various embodimentscan allow the portion of the scintillator assembly 300 facing theoptical system 400 to have nothing intervening in the space between thescintillator assembly 300 and the optical system 400. In these variousembodiments, the mount 350 securing the scintillator assembly 300 may bemoved to place the scintillator assembly 300 in very close proximity orin direct contact with the optical system 400.

Referring now to FIG. 17, in this embodiment, the combination of object200-I and scintillator assembly 300 can be translated, rotated ortilted, as shown in the illustration. The object 200-I in this tiltedconfiguration can then be rotated about the z-axis to allow images atmultiple angles to be collected.

In a configuration such as that shown in FIG. 17, the optical system400-MT may be further modified from the optical system 400 used forimaging where the scintillator is perpendicular to the optical axis ofthe optical system 400 (normal incidence imaging), as was shown in FIGS.6, 11 and 16. The optical system 400-MT may also be further modifiedfrom the optical system 400-M that was used for imaging an object wherethe scintillator is supported by a membrane 354, as was shown in FIG.17. The optical system 400-MT will need to collect an image of thescintillator 310 while it is supported by a membrane 354 and is tiltedoff axis. In some embodiments, as will be known to those skilled in theart, this can be achieved by using a design for the optical system400-MT that produces an image with enhanced depth of focus.

Referring to FIG. 18, in some embodiments, this can be achieved by usinga design for the optical system 400-MT in which the image plane of theoptical system 400-MT may be tilted at an angle to the x-y plane. Insome embodiments, the image sensor 510 can be placed at this tiltedimage plane. As was the case for moving the mount 250-M, connector 358and controller 359, analogous to connector 258 and controller 259, canbe used to move the object 200-I and scintilaltor assembly 300combination. The motions may be the analogous translations, rotations,and tilts as discussed above. If the mount 350-M is rotated to collectimages at different angles of incidence, the image sensor 510 will needto be correspondingly rotated to ensure the image remains in focus.

Referring now to FIG. 19, in other embodiments, one set of ends for afiber optic bundle 505 can be placed at the image plane 501 of theoptical system 400-MT, and the other ends of the fiber bundle 505 placedin close proximity to the modified image sensor 510-F (which may bemodified from the image detector 500 of other embodiments to accommodatecoupling to the fiber bundle) of the detector 500-F. In this embodiment,if the mount 350-M is rotated to collect images at different angles ofincidence, the ends of the fiber optic bundle 505 may need to becorrespondingly rotated to ensure the image remains in focus.

Referring now to FIG. 20, the emission of photons by the scintillator310 is typically uniform in all directions. However, if the scintillator310 and support 350 are tilted, because the angles encountered by theemitted photons at the face of the tilted support 350 are not uniform,the light emerging from the support 350 may be attenuated more for someangles than others, distorting the image. For some tilt angles, lightemitted along the optic axis of the objective lens may be internallyreflected.

In FIG. 20, scintillator emission that exits the support 350 indirections near normal incidence 411-A to the plane of the support 350will be mostly transmitted through the support-air interface. However,scintillator emission that exits the support 350 in directions far fromnormal incidence 411-B to the plane of the support 350 will be muchweaker, and have much more of the light reflected back into the support350 at the support-air interface. The reflection and transmissioncoefficients can be calculated from the relative indices of refractionfor these materials, as will be known to those skilled in the art.

Referring now to FIG. 21, in some embodiments the non-uniformity of thelight transmitted through the support-air interface can be addressed bya replacing the support 350 with a prism 405. In some embodiments, thisprism fills the optical path between the scintillator 310 and theoptical system 400-P (designed to anticipate the prism 405 in theoptical path). Because the bottom of the prism is perpendicular to theoptical axis of the system 400-P, these rays are no longer internallyreflected and are therefore transmitted into the optical system 400-P.

In some embodiments, the modifications in design for the optical system400-P may include design for a larger working distance, to accommodatethe prism in the optical path. In some embodiments, the scintillatorwill be attached to the prism 405 using a index-matching optical qualityadhesive. In some embodiments, the prism 405 may be used in conjunctionwith a support 350 for the scintillator 310 as well. In this case, theprism 405 can be index-matched to the support 350 to reduce reflectionsfrom the support-prism interface. In some embodiments, the support 350will be attached to the prism 405 using an index-matching opticalquality adhesive.

In some embodiments, the optical properties of the prism 405 will beindex-matched to the scintillator, so that no additional reflectionsoccur at the scintillator—prism interface. With a suitable design of theprism comprising one face towards the optical system 400-P, a clear viewof the emitted light is provided, and the image is formed with lessdistortion. In some embodiments, the prism 405 will be index matched tothe elements in the optical system 400-P to act as a solid immersionlens. In some embodiments, the prism may comprise LuAG. LuAG has arefractive index n=1.84 at a wavelength of 535 nm, allowing the opticalsystem 400 to be designed with LuAG elements to have an effectiveNA≈1.75. This can have the effect of improving the achievable resolutionof the optical system 400-P.

Scintillator Variations.

Some embodiments of the invention may comprise additional variations ofthe elements of the scintillator assembly 300.

In some embodiments, providing a coating 320 on the scintillator 310 canalso reduce the impact of dust on the image. As illustrated in FIG. 22A,unless operated in an ultra-clean environment, one or more dustparticles 333 can settle on the surface of the scintillator assembly300. Light emitted by the scintillator 310 in response to the absorptionof x-rays is emitted in all directions, and some emission 411-Rpropagates back towards the object 200. If there is no coating on thescintillator-air interface, the dust can settle directly onto thescintillator 310 itself. The emitted light 411-R can then scatter offthe dust particle 333 back towards the optical system 400 as scatteredlight 411-S. The dust particle 333 can then appear as a bright, oftenout-of-focus spot in the image that has nothing to do with the object200 being examined.

If, however, as shown in FIG. 22B, the scintillator assembly 300 has acoating 320 made from a material such as carbon black as manufactured bythe Cabot Corporation of Boston, Mass., light 411-R emitted towards thedust particle 333 is absorbed as it passes through the coating 320, andthe attenuated light that scatters off the dust particle 333 is in turnfurther attenuated as it again passes through the coating 320 andbecomes light 411-SA propagating towards the optical system 400. The“noise” in the image from unwanted particles can therefore besignificantly reduced.

As shown in FIG. 22C, in some embodiments, the coating 320-R maycomprise a uniform layer of a reflective metal such as silver (Ag) oraluminum (Al) that can more uniformly reflect all light from thescintillator-coating interface back into the scintillator 310 and on tothe optical system 400. This can have the dual advantage of reducing thesusceptibility to scattering from dust particles 333 which may settle onthe coating, while adding additional light to the image. Scintillatorlight 411-O emitted towards the object 200 will reflect off the coating320-R and propagate back towards the optical system as reflected emittedlight 411-O1. As long as the scintillator 310 is thin enough, thereflected emission 411-O1 will be collected by the optical system and beimaged close to the directly emitted visible photons 411 from thescintillator. Likewise, the emission at greater angles 411-R willreflect away from the optical system 400 as light 411-R1, and dustparticles 333 will have little effect on the image.

In some embodiments, the scintillator coating 320 is fabricated fromcarbon as a coating of diamond or a diamond-like carbon (DLC) fabricatedby chemical vapor deposition (CVD). In some embodiments, a coating ofsapphire (Al₂O₃) may also be used. In a similar manner to the way thecoating 320 prevents dust from adding unwanted light into the image, thecoating 320 may also prevent light from the scintillator from scatteringback from the object 200 being examined as well. The coating 320 maycomprise layer of silver, aluminum or carbon deposited by evaporation orsputtering. The coating 320 may also comprise a layer of nano-particles.

As discussed above, the scintillator assembly 300 may also comprise asupport 350. In some embodiments the support may be fabricated from asimple microscope slide. In other embodiments, the support 350 may befabricated using an optical flat. In some embodiments, the support 350may also be fabricated from a material designed to transmit UV light,such as fused silica or quartz.

Optical System Variations.

Some embodiments of the invention may comprise additional variations ofthe elements of the optical system 400.

In some embodiments, the lenses of the optical system 400 may compriseUV compatible optical materials, such as fused silica or quartz. In someembodiments, the lenses of the optical system 400 may comprise radiationresistant optical materials, for example glasses doped with Cerium Oxide(CeO₂) such as SCHOTT BK7G18, manufactured by SCHOTT Glasswerke ofMainz, Germany.

In some embodiments, the optical system 400 is secured or fastened tothe scintillator assembly 300 to prevent relative motion. In someembodiments, as illustrated in FIG. 23, the optical system 400-S can bedesigned so that the scintillator 310 can be mounted onto the face ofobjective lens 410. In such an embodiment, the lens material and thematerial used for the scintillator 310 may be selected to have matchedrefractive indices and/or matched dispersion properties. Thescintillator 310 may be attached to the objective lens 410 using anindex-matching adhesive. In some embodiments, the scintillator 310 asattached to the housing of the objective lens 410. In some embodiments,the scintillator 310 attached to the objective lens 410 or its housingmay have a coating 320, as described above. In some embodiments, thescintillator 310 attached to the objective lens 410 or its housing mayhave an additional support 350, as described above, which is alsoattached to the objective lens 410 or its housing.

In some embodiments, such as the embodiment described above in which thespace between the scintillator 310 and the optical system 400-Pcomprises a prism 405, or in other designs for the optical system 400 inwhich a “solid immersion lens” is used, the materials for thescintillator, prism or solid immersion lens, as well as the lenses ofthe optical system 400, may be selected to have matched refractiveindices. In some embodiments, the materials for the scintillator, prismor solid immersion lens, as well as the lenses of the optical system400, may be selected to have matched dispersion characteristics over adefined wavelength range.

The optical system may be designed to bend the optical path, so that theimage is not formed along the same axis as the direction in which thex-rays are propagating. This can further isolate the image detector 500from potential harmful exposure to x-rays.

Referring again to FIG. 19, one approach to remove the image detectorfrom the x-ray beam path is the use of a fiber optic bundle 505 or arrayto collect the image formed by the optical system 400 and convey it tothe modified image detector 500-F.

In another embodiment, an optical path comprising a beamsplitter ormirror can be used to reflect the optical portions of the image onto animage detector 500 while transmitting the x-rays.

Referring now to FIG. 24, additional, elements 425 in the optical systemmay also be used to introduce additional properties to the image. Insome embodiments, additional elements 425 may comprise a color filter,to select specific wavelengths emitted by the scintillator 310. Thisfilter may, for example, select visible scintillator emission forimaging while blocking or absorbing UV emission. This filter may, forexample, select UV scintillator emission for imaging while blocking orabsorbing visible emission.

In some embodiments, as illustrated in FIG. 24, the optical system 400can be governed by a controller 459 through a connector 458. The opticalsystem controller 459 may manipulate mechanical elements of the opticalsystem 400 to change the focus, the tilt of the image plane, tocoordinate lens rotation with the rotation of the object 200, to adjustinternal apertures to change the image intensity, to adjust filters orother additional elements 425, and other lens adjustments that will beknown to those skilled in the art.

In some embodiments, the signals from the optical system controller 459will be coordinated with signals to the mount 250 provided by the mountcontroller 259. In some embodiments, the signals from the optical systemcontroller 459 will be coordinated with signals to the shutter 130provided by the shutter controller 139. In some embodiments, the signalsfrom the optical system controller 459 will be coordinated with signalsto the x-ray source 100 provided by the source power supply 119. In someembodiments, some or all of the coordination of the various controllerswill be directed by programs run using the one or more computer systems700.

In some embodiments, the control programs for the optical system 400executed using the one or more computer systems 700 will have auto-focusalgorithms that adjust the image for best contrast and definition. Insome embodiments, the control programs for the optical system 400executed using the computer system 700 will have look-up tables for apre-focus map. In some embodiments, the control programs for the opticalsystem 400 executed using the computer system 700 will have coordinatedmotions for both the object 200 and mount 250 and the optical system400. In some embodiments, the control programs for the optical system400 executed using the computer system 700 will have alignmentalgorithms to allow a specific region of an object 200 to be recognizedand examined.

Detector Variations.

Some embodiments of the invention may comprise additional variations ofthe elements of the image detector 500.

In some embodiments of the invention, images are obtained continuouslywhile the object 200 is moving using a time-delay and integration (TDI)device or method. The TDI detector may be based on a CCD camera that issynchronized with the motion of the mount 250 or stage.

In some embodiments, the image detector 500 will produce a signal withcomponents corresponding to a pixel number and a correspondingintensity. In some embodiments, the image detector 500 will produce asignal with components corresponding to coordinate locations and acorresponding intensity. In some embodiments, this signal is transmittedover a connector 558 to a system of electronics 600 for additionalsignal processing and possible display.

In some embodiments of the invention, the system of electronics 600associated with the detector will analyze the image signal and performadjustments such as image alignment, brightness adjustment, contrastenhancement, digital filtering, or fast Fourier transforms (FFTs). Insome embodiments, single images or multiple images will be analyzed toallow 3D reconstructions of the structures in the object, includingalgebraic reconstructions, backpropagation algorithms, adaptive kernelfiltering, computed laminography (CL), as well as other reconstructiontechniques that are based on some degree of pre-knowledge of theintended layout. Such pre-knowledge may comprise design databases suchas GDS-II or OASIS data, specifications for planarity of layers,material properties, and the anticipated geometry and number of layers.

In some embodiments, the system of electronics 600 will additionallycomprise a display that allows an operator to view the image in realtime. In some embodiments, the system of electronics will comprisecontrol programs that communicate operator input or automaticallygenerated input to the various power supplies and controllers 119, 139,259, and 459 for the x-ray source 100, the shutter 130, the mount 250holding the object 200, and the optical system 400. In some embodiments,the network that interfaces the computer system 700 with the variouscontrollers 119, 139, 259, 459, and 600 may be an Ethernet network. Insome embodiments, the images may be accessed by the computer system 700using an internet connection (via packets) or a serial bus (e.g. USB2.0).

Control programs and image analysis procedures may comprise theoperation of software programs for equipment control and image analysissuch as those written in LabVIEW® by National Instruments Corp. ofAustin, Tex., MatLab® by MathWorks, Inc. of Natick, Mass., or publicdomain image processing programs such as ImageJ, developed by theNational Institutes of Health in Bethesda, Md.

Computer System Detail and Variations.

Some embodiments of the invention may comprise additional variations ofthe elements of the one or more computer systems 700.

In some embodiments, a computer system 700 will comprise stored controlprograms that communicate instructions to the various power supplies andcontrollers 119, 139, 259, 459 for the x-ray source 100, the shutter130, the mount 250 holding the object 200, and the optical system 400,as well as for collecting corresponding images from the system ofelectronics 600 gathering image signals from the image detector 500.These instructions can be pre-programmed recipes for specificmeasurement sites, or a general program for inspection of an entireobject 200 or portion thereof.

In some embodiments, the computer system 700 may also be used forprocessing images. This may include image alignment, sub-pixelinterpolation, or modification of the image histogram such as brightnessor contrast adjustments.

In some embodiments, the computer system 700 may also be used forthree-dimensional image reconstruction. In this case, two or more imagesare used to generate a three-dimensional representation or model of theobject being examined. The images may be obtained by changing the objectorientation with respect to the x-ray beam (or vice versa), for example.These reconstructions may comprise any one of, or a combination of,algebraic reconstructions, backpropagation methods, or Fourier transformmethods. Furthermore, these reconstruction methods may incorporateknowledge of the object structure or materials to aid in thereconstruction. For example, the knowledge of the number of interconnectlayers may be used to improve the reconstruction.

FIG. 25 illustrates a block diagram of an exemplary computer system thatcan serve as a platform for portions of embodiments of the presentinvention. Computer system 700, as described above, can comprise a bus7007 which interconnects major subsystems of computer system 700, suchas a central processing unit (CPU) 7000, a system memory 7010 (typicallyrandom-access memory (RAM), but which may also include read-only memory(ROM), flash RAM, or the like), an input/output (I/O) controller 7020,one or more data storage systems 7030, 7031 such as an internal harddisk drive or an internal flash drive or the like, a network interface7700 to an external network 7777, such as the Internet, a fiber channelnetwork, or the like, an equipment interface 7600 to connect thecomputer system 700 to a network 607 of other electronic equipmentcomponents, and one or more drives 7060, 7061 operative to receivecomputer-readable media (CRM) such as an optical disk 7062, compact discread-only memory (CD-ROM), compact discs, floppy disks, universal serialbus (USB) thumbdrives 7063, magnetic tapes and the like. The computersystem 700 may also comprise a keyboard 7090, a mouse 7092, and one ormore various other I/O devices such as a trackball, an input tablet, atouchscreen device, an audio microphone and the like. The computersystem 700 may also comprise a display device 7080, such as acathode-ray tube (CRT) screen, a flat panel display or other displaydevice; and an audio output device 7082, such as a speaker system. Thecomputer system 700 may also comprise an interface 7088 to an externaldisplay 7780, which may have additional means for audio, video, or othergraphical display capabilities for remote viewing or analysis of resultsat an additional location.

Bus 7007 allows data communication between central processor 7000 andsystem memory 7010, which may comprise read-only memory (ROM) or flashmemory, as well as random-access memory (RAM), as previously noted. TheRAM is generally the main memory into which the operating system andapplication programs are loaded. The ROM or flash memory can contain,among other code, the basic input/output system (BIOS) that controlsbasic hardware operation such as the interaction with peripheralcomponents. Applications resident with computer system 700 are generallystored on storage units 7030, 7031 comprising computer readable media(CRM) such as a hard disk drive (e.g., fixed disk) or flash drives.

Data can be imported into the computer system 700 or exported from thecomputer system 700 via drives that accommodate the insertion ofportable CRM drives, such as an optical disk 7062, a USB thumbdrive7063, and the like. Additionally, applications and data can be in theform of electronic signals modulated in accordance with the applicationand data communication technology when accessed from a network 7777 vianetwork interface 7700. The network interface 7700 may provide a directconnection to a remote server via a direct network link to the Internetvia an Internet PoP (Point of Presence). The network 7700 may alsoprovide such a connection using wireless techniques, including a digitalcellular telephone connection, a Cellular Digital Packet Data (CDPD)connection, a digital satellite data connection or the like.

Many other devices or subsystems (not shown) may be connected in asimilar manner (e.g., document scanners, digital cameras and so on).Conversely, all of the devices shown in FIG. 25 need not be present topractice the present disclosure. In some embodiments, the devices andsubsystems can be interconnected in different ways from that illustratedin FIG. 25. The operation of a computer system 700 such as that shown inFIG. 25 is readily known in the art and is not discussed in furtherdetail in this Application.

Code to implement the present disclosure can be stored oncomputer-readable storage media such as one or more of: the systemmemory 7010, internal storage units 7030 and 7031, an optical disk 7062,a USB thumbdrive 7063, one or more floppy disks, or on other storagemedia. The operating system provided for computer system 700 may be anyone of a number of operating systems, such as MS-DOS®, MS-WINDOWS®,UNIX®, Linux®, OS-X® or another known operating system.

Moreover, regarding the signals described herein, those skilled in theart will recognize that a signal can be directly transmitted from oneblock to another, between single blocks or multiple blocks, or can bemodified (e.g., amplified, attenuated, delayed, latched, buffered,inverted, filtered, or otherwise modified) by one or more of the blocks.

Further Embodiments Using the X-Ray Imaging System.

So far, this disclosure has described embodiments of an x-ray systemthat can rapidly collect images of high quality at high resolution witha large field of view. The images so generated can reveal informationabout the internal structures of an IC, a chip package or assemblywithout damaging the object itself. As a result, these electronic imagescan be used for various metrology systems and inspection systems. Thesemetrology and inspection results can in turn be used as a part ofmanufacturing process control systems using statistical process control(SPC), or for process yield management and improvement systems thatenable manufacturing products with higher yield.

Metrology.

The images from the disclosed x-ray system may be used for metrology.This may include measuring the sizes and/or shapes of features in theobject being examined, such as the diameter or side-wall angle of TSVs.The metrology may also include measuring features at different places onthe object and comparing them to each other, or comparing them to astandard, as well as reporting the measurements.

The images may also be used to reverse-engineer the internal structureof the object being examined. For example, the images orthree-dimensional reconstruction may be used to generate a list ofelectrical connections or a file to be used for creating a reticle forprinting the circuits. The images may be used to detect changes in theobject structure from nominal. These images may also be used to identifycertain features in the object that may be of interest. They may be usedto reverse engineer a product, determining the materials and internalstructures of an object non-destructively.

FIG. 26 illustrates one embodiment of a method for conducting metrologyusing an x-ray system as disclosed in this Application.

This method for metrology 2000 has, as its first step 2001, theselection of an object to be examined. This object may be blank incomingmaterial before processing begins, or a partly or fully manufacturedintegrated circuit or portion thereof, a 2.5D IC or 3D IC package, asilicon interposer with TSVs, a C4 flip chip interconnect package, amulti-chip module (MCM), or any one of a number of the objects, devicesand structures disclosed in this Application, as well as others thatwill be known to those skilled in the art.

In the next step 2020, a particular position on the object is selectedfor measurement. This may be selected manually, or it may be selected byreference to a stored program or recipe stored in a Measurement RecipeDatabase 2300.

In the next step 2221, the object is mounted in the x-ray systemaccording to the disclosed invention, and one or more x-ray images arecollected. The x-ray system will typically comprise a source, preferablywith high x-ray flux, a mount to position the object, a scintillator, anoptical system, and an optical image detector, as has already beendisclosed in detail in this Application. In typical embodimentsaccording to the invention, the ratio of the source spot size to theresolution of the optical imaging system and detector combination willbe greater than 1, while the resolution will be less than 10 microns.

In the next step 2231, the one or more x-ray images are gathered and theimage data analyzed for certain features, such as CD measurements.Feature linewidths, diameters, shapes, thicknesses, depths, spacesbetween objects, line edge roughness, etc. may be calculated based onthe x-ray image data collected. Some of these calculations may be donemanually, but more commonly, a stored computer program comprising imageanalysis algorithms and image comparison procedures, as well as storedfiles of reference images and design databases, may be provided in aMeasurement Algorithm Database 2320. In some embodiments, thesealgorithms may include image processing algorithms, such as FourierTransforms, contrast enhancement, shape or pattern recognition, etc. Insome embodiments, these algorithms may be called automatically as partof the recipe for measurement stored in the Measurement Recipe Database2300. In some embodiments, these algorithms may combine data from two ormore images to compute 3D depth information. Other metrology protocolswill be known to those skilled in the art.

In the next step 2250, the results of the analysis of the image arestored as metrology results in a Results Database 2360. These resultsmay be indexed or stored with reference to the Measurement RecipeDatabase 2300 or the Measurement Algorithm Database 2320.

Once the images and measurements have been collected for one position onthe object, the next step 2255 comprises a determination of whether allpositions required by the recipe for object being examined have beenmeasured, or if the recipe requires additional measurements. If thedetermination is YES, a new position is determined and then selected onthe object according to the earlier mentioned step 2020, x-raymeasurements generated 2221, and the measurement results generated 2231and stored 2250, and the determination 2255 is again made. If thedetermination is NO, i.e. that all required measurement data for theobject has been gathered, the last step 2260 outputs the measurementresults, in some embodiments calling them from the Results Database2360. The output results can be in the form of a collection of data, orfurther prepared as a formatted report to be printed, filed and possiblyarchived and reviewed at a later time.

Although this is one embodiment of a metrology process using the x-raysystem according to the invention, it will be recognized that variationson this process will be known to those skilled in the art of metrology.In some embodiments, all x-ray images may be gathered before anyanalysis is carried out. In some embodiments, the process may beentirely automatic, governed by one or more computers. In someembodiments, the one or more computers controlling the metrology processmay also be one or more computers controlling the x-ray system itself.

This metrology process 2000 or similar variations may be used to examineindividual objects to determine their structure and properties. However,this metrology process 2000 or similar variations can be inserted into amanufacturing process as a form of process control. Such process controltechniques, such as statistical process control (SPC) or others thatwill be known to those skilled in the art, measure predefined structureson an ongoing basis and alert the operator when a process variable iseither out of specification, or is drifting out of specification. Often,a body of knowledge about the process will have been built up over thehistory of the manufacturing line, and the process control alerts can bea signal that triggers some predefined process improvement. For example,an alert that wafers or chips processed by a particular tool now havelinewidth variation that is increasing relative to its previousperformance may trigger preventive maintenance for that particular tool.

FIG. 27 illustrates one embodiment of a method for conducting processcontrol 2500 for a manufacturing process using the metrology process2000 comprising measurement using an x-ray system as disclosed in thisApplication.

In the initial step 2501, the manufacturing process is defined andidentified. This may be a small single unit process, such as a waferlithography stepper and track combination, or an entire multi-stepprocess for fabricating an entire integrated circuit, or a packagingprocess for assembling multiple integrated devices into one package. Themanufacturing recipe or recipes and the associated specification valuesand control limits may be stored in one or more Specification Databases2600.

Once the manufacturing line is operational, in the next step 2505, oneor more objects are fabricated according to the predefined process,calling on the Specification Database 2600 for recipes as needed. Theobject may be incoming material to the manufacturing process, apartially manufactured product, a test or pilot wafer, a fullymanufactured IC, a wafer prior to dicing, chips from a wafer afterdicing, chips partially or fully assembled in a 3D IC package, aninterposer, incoming packaging boards or material, partially mounted ICsin packages, a fully assembled IC package, or any one of a number ofproducts and by-products associated with a manufacturing process.

In the next step 2000, the metrology process disclosed above is executedto generate measurement results for the fabricated object using thex-ray system as disclosed. The Specification Database 2600 may providesome or all of the data required by the Measurement Recipe Database 2300to direct the metrology process.

The next step is the output step of metrology process 2000, which wasthe step of outputting measurement results 2260.

In the next step 2530, the measurement results are evaluated accordingto information provided by the specification database 2600, and theparticular process variables and parameters are determined and comparedto their historical values.

If this step 2530 determines that all processes are functioning withinthe predetermined parameters as defined in the Specification Database2600, then the determination is YES, and the product manufacturing 2599proceeds. The products, such as integrated circuits, IC packages, etc.,are within the predefined specification, and the execution of the methodfor conducting process control 2500 helps to identify problems beforesignificant amounts of material are manufactured incorrectly, and haveto be scrapped. The cost per working unit of the product is thereforereduced.

However, if this step 2530 determines that a measurement is currentlyout of specification, or that certain derived parameters, such as thestandard deviation of a process variable, are out of specification, orany one of a number of predefined conditions are met, then thedetermination is NO.

In this case, the next step 2540 is an evaluation of the deviantconditions, either manually or by automated means using one or morecomputers, and a determination of what might be changed to fix it. Insome embodiments, there may be two major classifications of problems:those arising from product DESIGN, and those arising from amanufacturing PROCESS.

DESIGN problems will typically appear repeatedly as systematic failuresfor parts when the design has the same configuration. One example of adesign problem is the bridging of interconnect lines that have beenfabricated too close together, i.e. when the space between the linescannot be resolved by the lithography stepper printing the lines.Another example of a design problem is when TSVs in an interposer havesimply been designed to be smaller than the manufacturing process canreliably support.

If the result of this step 2540 is a determination that there is aDESIGN problem, the next step 2560 is to redesign the object. For theexamples given above, the if two nearby lines are bridging, a new designwhich separates these lines will be created; likewise, if TSVs are toosmall, or have an un-manufacturable aspect ratio, a new design withlarger TSVs, or with multiple (i.e. redundant) vias for criticalconnections may be created.

Once the new design has been created, the next step 2595 is to fabricatethe re-designed object, and then proceed to again make measurements 2000with the x-ray system, output the measurement results 2260, and evaluatethe measurement results 2530 as before.

In some cases, a redesign may also require a step 2591 in which arevision to the manufacturing process is also made. This revision may inturn require a change to the data in the Specification Database 2600,which will now comprise recipes and specifications that correspond tothe re-designed product.

If the result of this step 2540 is a determination that there is aPROCESS problem, the next step 2550 is to determine any changes in themanufacturing process. For the examples given above, comparable processproblems can also occur. Two lines that are fabricated close to eachother may normally be printable, but a process may no longer be reliablyprinting them. This may indicate a focus error in one or more of thesteppers used to print the IC layer containing the line pairs. Likewise,vias that are normally manufactured reliably may now have internalvoids, making electrical contact unreliable. This may require a changein the copper deposition process for the TSVs, or the adaptation of anannealing process that reduces susceptibility to void growth.

In the next step 2591, the changes are made to the manufacturingprocess. Corresponding changes to the data in the Specification Database2600 may also be made, so that the Database 2600 will now compriserecipes and specifications that correspond to the re-engineered process.

Inspection.

The images from the disclosed x-ray system may be used for inspection.By comparing these gathered images to those from another nominallyidentical device, or to an idealized estimate of how the design shouldappear in the manufactured part, or by comparison with a pre-determinedset of design rules, defects can be identified, and the object underinvestigation set aside for further investigation.

The images or a reconstructed model may then be used to perform defectdetection on the object being examined. Defects may be classified ascritical or non-critical, or sorted by type. The location of defects maybe reported, as well a Pareto analysis of defects by size, shape,location or other relevant parameter. These results may be used forstatistical process control.

FIG. 28 illustrates one embodiment of a method for conducting inspectionusing an x-ray system as disclosed in this Application.

This method for inspection 3000 has, as its first step 3001, theselection of an object to be examined. This object may be blank incomingmaterial before processing begins, or a partly or fully manufacturedintegrated circuit or portion thereof, a 2.5D IC or 3D IC package, asilicon interposer with TSVs, a C4 flip chip interconnect package, amulti-chip module (MCM), or any one of a number of the objects, devicesand structures disclosed in this Application, as well as others thatwill be known to those skilled in the art.

In the next step 3020, a particular position on the object is selectedfor measurement. This may be selected manually, or it may be selected byreference to a stored program or recipe stored in an Inspection RecipeDatabase 3300.

In the next step 3221, the object is mounted in the x-ray systemaccording to the disclosed invention, and one or more x-ray images arecollected. The x-ray system will typically comprise a source, preferablywith high x-ray flux, a mount to position the object, a scintillator, anoptical system, and an optical image detector, as has already beendisclosed in detail in this Application. In typical embodimentsaccording to the invention, the ratio of the source spot size to theresolution of the optical imaging system and detector combination willbe greater than 1, while the resolution will be less than 10 microns.

In the next step 3231, the one or more x-ray images are gathered and theimage data analyzed for indications of defects. The determination of thepresence or absence of defects may be carried out by conducting ananalysis of the data in the x-ray image alone, evaluating the x-rayimage data for the signature of various known defects (such as blackdots for voids, anomalous bright spots, etc.) using algorithms that arethe same as, or similar to, those used for metrology analysis asdescribed above. The determination of the presence or absence of defectsmay be carried out by comparing the image data to data previouslygathered for a similar section of another object (such as is done indie-to-die inspection), or it may be carried out by comparison to acorresponding portion of a reference database of design data (such as isdone in die-to-database inspection). Some of these calculations may bedone manually, but more commonly, a stored computer program comprisingimage analysis algorithms and image comparison procedures, as well asstored files of reference images and design databases, may be providedin a Reference Database 3320. In some embodiments, these algorithms mayinclude image processing algorithms, such as Fourier Transforms,contrast enhancement, shape or pattern recognition, etc. In someembodiments, these algorithms may be called automatically as part of therecipe for measurement stored in the Inspection Recipe Database 3300. Insome embodiments, these algorithms may combine data from two or moreimages to compute 3D depth information. Other inspection protocols willbe known to those skilled in the art.

In the next step 3231, the data corresponding to the one or more x-rayimages of the object will be analyzed for potential defects, using anyor all of the techniques mentioned above. If none of the analysesconducted on the one or more x-ray images suggests the presence of adefect in the location of the object corresponding to the x-ray image,the determination for the set of locations is CLEAR. If at least oneanalysis of the image shows an anomaly, the determination for the set oflocations is DEFECT.

If the determination for an x-ray image is CLEAR, the next step 3255comprises a determination of whether all positions required by therecipe for object being examined have been measured, or if the reciperequires additional measurements. If the determination is YES, a newposition is determined and then selected on the object according to theearlier mentioned step 3020, x-ray measurements are generated 3221, andthe inspection results for the new location evaluated 3231 and thedetermination 3255 is again made.

If the determination is DEFECT, i.e. one of the analysis proceduresindicates that the there is a potential defect at the location, furtheranalysis of the image is carried out.

In this case, the next step 3431 is the comparison of the signature ofthe result of the defect analysis with a Defect Database 3340, which,among other things, may comprise known signatures of known types ofdefects. For example, an irregular, skinny blob detected within astructure corresponding to a TSV may represent a signature of a voidwithin the copper. As another example, the comparison of an image with acorresponding portion of the design database may indicate that ainterconnect line should be present when there is no correspondingfeature in the x-ray image.

If the determination of the comparison step 3431 is that there is NOrecognition of a particular defect type, the potential defect at thislocation is determined to be NEW. The next step 3480 will be will be tocatalog the data associated with this anomalous result, and in someembodiments also storing this new data in the Defect Database 3340.After this, the next step 3255 comprises a determination of whether allpositions required by the recipe for object being examined have beenmeasured, or if the recipe requires additional measurements. If thedetermination is YES, a new position is determined and then selected onthe object according to the earlier mentioned step 3020, x-raymeasurements are generated 3221, and the inspection results for the newlocation evaluated 3231 and the determination 3255 is again made. If thedetermination is NO, then the next step 3260 may comprise outputting thefinal results for the inspection.

If the determination of the comparison step 3431 is the recognition of aparticular defect type, the location is determined to be KNOWN. The nextstep 3450 will be the prediction of any failure mode known to occur withthis particular defect type. This prediction 3450 may be carried outwith reference to a Failure Database 3360, which may compriseinformation on historical records or theoretical models for the object,process, and product being inspected.

Once the failure mode is predicted, steps to prevent future defects andproduct failures may be made. In the next step 3490, a correction to theprocess may be recommended, either by an automated computer programbased on historical data for the process, or based on an engineeringevaluation of the defect type and failure mode.

Once the correction is recommended, the next steps are two-fold. On theone hand, one of the next steps 3260 comprises outputting the inspectionresults, typically along with the recommended changes. On the otherhand, one of the next steps 3255 comprises a determination of whetherall positions required by the recipe for object being examined have beenmeasured, or if the recipe requires additional measurements. If thedetermination is YES, a new position is determined and then selected onthe object according to the earlier mentioned step 3020, x-raymeasurements are generated 3221, and the inspection results for the newlocation evaluated 3231. If the determination is NO, then the next step3260 may comprise outputting the final results for the inspection.

The output results 3260 can be in the form of a collection of data, orfurther prepared as a formatted report to be printed, filed and possiblyarchived and reviewed at a later time. They may contain a list ofidentified electrical connections (such as a netlist), a listing ofgeometric polygons (such as a layout), a listing of locations and thenumber of defects detected, a listing such as a Pareto chart of thetypes of defect detected. Counts of both defect and regular featuressizes and shapes may also be included. Means may be provided for manualreview of defects, or for an automated review of defect.

Although this is one embodiment of an inspection process using the x-raysystem according to the invention, it will be recognized that variationson this process will be known to those skilled in the art of inspection.In some embodiments, all x-ray images may be gathered before anyanalysis is carried out. In some embodiments, the process may beentirely automatic, governed by one or more computers. In someembodiments, the one or more computers controlling the inspectionprocess may also be one or more computers controlling the x-ray systemitself.

This inspection process 3000 or similar variations may be used toexamine individual objects to determine their structure and properties.However, this inspection process 3000 or similar variations can beinserted into a manufacturing process as a form of yield management.Such yield management techniques will be known to those skilled in theart, and are commonly used to inspect manufactured products or samplesfrom a manufacturing line on an ongoing basis, and alert the operatorwhen a defects or anomalies are beyond certain specified limits. Often,a body of knowledge about the process will have been built up over thehistory of the manufacturing line, and the defect statistics can be usedto produce a signal that triggers some predefined process improvement.For example, an alert that wafers or chips processed using a particulartool now have an increase in dust particles larger than 10 microns maytrigger preventive maintenance for that particular tool.

FIG. 29 illustrates one embodiment of a method for conducting yieldmanagement 3500 using the inspection process 3000 comprising inspectionusing an x-ray system as disclosed in this Application.

In the initial step 3501, the manufacturing process is defined andidentified. This may be a small single unit process, such as a waferlithography stepper and track combination, or an entire multi-stepprocess for fabricating an entire integrated circuit, or a packagingprocess for assembling multiple integrated devices into one package. Themanufacturing recipe or recipes and the associated specification valuesand control limits may be stored in one or more Manufacturing Databases3600.

Once the manufacturing line is operational, in the next step 3505, oneor more objects are fabricated according to the predefined process,calling on the Manufacturing Database 3600 for recipes as needed. Theobject may be incoming material to the manufacturing process, apartially manufactured product, a test or pilot wafer, a fullymanufactured IC, a wafer prior to dicing, chips from a wafer afterdicing, chips partially or fully assembled in a 3D IC package, aninterposer, incoming packaging boards or material, partially mounted ICsin packages, a fully assembled IC package, or any one of a number ofproducts and by-products associated with a manufacturing process.

In the next step 3000, the inspection process disclosed above isexecuted to generate inspection results for the fabricated object usingthe x-ray system as disclosed. The Manufacturing Database 3600 mayprovide some or all of the data to direct the inspection process.

The next step is the final step of the inspection process 3000, whichwas the step of outputting results 3260.

In the next step 3530, the inspection results are evaluated to see ifthe process can be labeled “Defect Free”, according in part to thedefinitions and specifications provided by the Manufacturing Database3600. This step may comprise determining particular defect statisticsand yield parameters and comparing them to their historical values.

If this step 3530 determines that all processes are functioning withinthe predetermined defect and yield parameters as defined in theManufacturing Database 2600, then the determination is YES, the processcan be labeled “Defect Free”, and the product manufacturing 3599proceeds. The products, such as integrated circuits, IC packages, etc.,are within the predefined yield, and the execution of the yieldmanagement process 3500 helps to identify problems before significantamounts of material are manufactured incorrectly, and have to bescrapped. The cost per working unit of the product is therefore reduced.

However, if this step 3530 determines that some portion of the processis not functioning within the predetermined defect and yield parametersas defined in the Manufacturing Database 2600, or any one of a number ofpredefined conditions are met, then the determination is NO, the processis not “Defect Free”.

In this case, there may be at least two possible the next steps 3580,3590 based on the results 3480, 3490 of the inspection process 3000. Ifone or more anomalies were cataloged in the previous step 3480 ofinspection process 3000, one of the next steps 3580 comprises analyzingthe detected anomalies, either manually or automatically using programsfor defect analysis and pattern recognition. One example of suchanalysis may be tabulating the locations of a set of defects to identifya cluster that may indicate a piece of equipment is occasionallyscratching a wafer. Although the individual pits and other defectsindividually may only appear locally random when considered one-by-one,an analysis of the cluster may reveal the characteristic pattern of ascratch.

Likewise, if one or more process corrections were recommended in theprevious step 3490 of inspection process 3000, one of the next steps3590 comprises tabulating the process corrections, either manually orautomatically using programs for defect analysis and patternrecognition.

Once the steps of analyzing the anomalies 3580 and tabulating thecorrections 3590 have been completed, the next step 3550 is anevaluation of the deviant conditions, either manually or by automatedmeans using one or more computers, and a determination of what might bechanged in the manufacturing process. For example, if scratches onwafers from one particular tool are being consistently detected, it maybe recommended that the deviant tool may be removed from themanufacturing process until the indicated mechanical problem with thewafer handling stage can be fixed.

In the next step 3591, the changes are actually implemented in themanufacturing process. Corresponding changes to the data in theManufacturing Database 3600 may also be made, so that the Database 3600will now comprise recipes and specifications that have been updated withthe new information.

Metrology and Inspection Variations.

Some embodiments of the invention may comprise additional variations ofthe elements of the metrology 2000 and inspection 3000 processes, aswell as the associated methods for process control 2500 and yieldmanagement 3500.

Several embodiments of the invention can be used, depending on theimaging properties of the detector and the design of the stage thatholds the object to be examined.

In some embodiments of the invention, multiple images of the object orportions thereof may be taken with different x-ray energy spectraldistributions. These multiple images may be combined, subtracted orotherwise processed numerically to produce a new image that has can makepotential defects more apparent.

In some embodiments of the invention, the images of the entire object tobe investigated, or images of portions of the object to be investigated,or 3D reconstructions of the object to be investigated, can be comparedto stored reference data, typically data representing a correctlymanufactured object. The stored reference data can comprise previouslycollected images, or stored information representing what is expectedfor a correctly manufactured object, or a set of mathematical orgeometric rules that a correctly manufactured object must follow.

In some embodiments of the invention, when discrepancies with the storedreference data are identified, further image processing and analysis canbe carried out to attempt to classify the discrepancies as correspondingto particular types or classes of defects. In some embodiments of theinvention, additional imaging at higher resolution or using additionalimaging angles for the incident x-ray beam may be performed to furtheridentify or characterize a potential defect.

In some situations, particularly with more elaborate structures such asmultiple ICs or ICs and interposers stacked in a 2.5D or a 3Dconfiguration, an embodiment of the invention can be used to examine theconfiguration prior to completing the bonding of the configuration, toinsure the components have been correctly aligned. It can also be usedas a component of a system to not only examine and inspect, but to alignand bond these multi-chip structures.

In some situations, the inspection system may be used to align toobjects before bonding or otherwise connecting them.

Some embodiments of the invention also include a method of manufacturingusing the apparatus described in this specification.

Some embodiments of the invention also include devices manufacturedusing the apparatus described in this specification, in which themanufacturing process for the product uses the apparatus to maintain theprocess within a process window or above a certain product yield, and inwhich the process includes metrology or defect detection or statisticalprocess control.

In some embodiments of the invention, the images and measurements may beused to adjust downstream processes in real time or near real time inorder to improve manufacturing yields.

In some embodiments of the invention, the images and measurements may beused to identify process variations, variation in incoming materials,changes in the condition of manufacturing equipment, or changes in themanufacturing recipe or process set up into the manufacturing equipment.

In some embodiments of the invention, the images and measurements may beused to screen defective or non-complying materials from themanufacturing line to prevent further destruction of other materialssuch as expensive active silicon devices.

In some embodiments of the invention, the images and measurements may beused to check the alignment between a via in an interposer or chip and acapture pad on the surface of the interposer or chip. The capture padmay also be used as a connection to the next device or interposer.

In some embodiments of the invention, the images and measurements may beused to detect voids or the absence of fill material in vias so as toreject the parts from manufacturing, or to determine if the voids are afactor in the long-term reliability of the component or system.

In some embodiments of the invention, the images may be taken as part ofan alignment process between a chip and an interposer prior to bondingor attaching the individual components. Based on these images, theprocess of alignment and bonding can be adjusted to improve the accuracyand quality of these connections. Other embodiments of the inventionallow real time feedback to alignment tools in aligning dice orinterposers.

In some embodiments of the invention, the images and measurements may beused to inspect the shape and dimensions of solder used to connectdevices or interposers. These inspections may be used to control themanufacturing process or screen out defective material. The presence ofsome patterns of solder after bonding may be used to detect impropersolder joints including joints in which the solder is not continuousbetween the two connection points and is therefore not a usefulconductor of electricity or heat. In other embodiments, multiple solderreflow processes may be utilized to repair or improve solder connectionsthat are determined to be non-complying with manufacturing or productspecifications based on results of inspection with the system accordingto the invention.

In some embodiments of the invention, the images and measurements may beused to determine the relative deviation in position and dimensions ofmultiple layers of metal lines, bumps, pads, or connecting layers in astack of chips and interposers.

Advantages of the Invention: Inspection Speed.

A significant advantage of this invention is that an extended source ofx-rays can be used, increasing the available flux of x-rays used forimaging. This in turn increases the throughput possible for the system.Put another way, in the time to acquire a single inspection image with aPPM system, the proposed invention can acquire over 300,000 images withthe same resolution.

Consider the following comparison with the PPM x-ray system. The time toacquire an image depends on the flux Φ of x-rays:T _(acquire)=(P _(#) ×X _(P))/Φwhere P_(#) is the number of pixels, X_(P) is the number of x-rays perpixel, and Φ is the x-ray flux. The x-ray flux from a point source is:Flux=Φ=β×Ω×S _(A)where β is the point source brightness, Ω is the angular distribution inmrad² and S_(A) is the point source area S_(A)=πr². The source spot sizefor x-ray systems is typically defined using the ASTM standard SE-1165[“Standard Test Method for Measurement of Focal Spots of IndustrialX-Ray Tubes by Pinhole Imaging,” ASTM Committee E-7 on NondestructiveTesting, May 15, 1992].

A typical x-ray source brightness β isβ=10⁸ x-rays/sec/mm²/mrad².To avoid parallax errors in automated inspection, the PPM x-ray beamshould be well collimated; a divergence of 20 mrad is typical. For apoint source withΩ=(20 mrad)²=400 mrad²and a source spot diameter d=2r=1 μm=10⁻³ mm, the flux is given by:

$\begin{matrix}{{Flux} = \Phi} \\{= {\beta \times \Omega \times S_{A}}} \\{= {10^{8} \times 400 \times \pi \times \left\lbrack {0.5 \times 10^{- 3}} \right\rbrack^{2}\mspace{14mu} x\text{-}{{rays}/\sec}}} \\{= {400 \times \pi \times 0.25 \times 10^{8} \times \left\lbrack 10^{- 3} \right\rbrack^{2}\mspace{14mu} x\text{-}{{rays}/\sec}}} \\{= {400 \times \pi \times 25\mspace{14mu} x\text{-}{{rays}/\sec}}} \\{= {31\text{,}416}} \\{= {3.14 \times 10^{4}\mspace{14mu} x\text{-}{{rays}/{\sec.}}}}\end{matrix}$A typical x-ray image sensor may have 512×512 pixels that need 1,000x-rays/pixel for image formation. An image for a PPM system willtherefore be collected in approximately 8,350 seconds, or 2.3 hours.

On the other hand, keeping the same source brightness, but illuminatingwith a larger source spot size according to the invention dramaticallyincreases the x-ray flux illuminating the object. As an example, assumea source with a 1 mm diameter (r=0.5 mm) separated by 100 mm from theobject and, furthermore, assume that the distance from the object toscintillator is 100 microns. The angular divergence of the x-ray beam isgiven by:α=1 mm/100 mm=10 mrad,makingΩ=100 mrad².The spot area is =π×[0.5]²=0.785 mm², so the flux becomes:

$\begin{matrix}{{Flux} = \Phi} \\{= {10^{8} \times 100 \times 0.785\mspace{14mu}{{photons}/\sec}}} \\{= {7.85 \times 10^{9}\mspace{14mu}{{photons}/\sec}}}\end{matrix}$which is higher than the PPM configuration by a factor of 250,000 times.Therefore, the same 512×512 image (with 1,000 x-rays per pixel) can nowbe produced at high speed and, for example, may now have aproportionally faster image collection time of approximately 33 msec.

As a practical matter, the throughput enhancement may be further reducedby a factor of between 2 and 10 from this number. A PPM imaging systemcan detect x-rays in the enlarged shadow image directly with a CCD x-raydetector, which can have a quantum efficiency between 50% to 100%. Thetypical x-ray CCD array comprises an array of pixels, with a pixel sizeof approximately 100 μm×100 μm.

In comparison, the high-resolution direct-shadow images for the systemof the disclosed invention come from an extended x-ray source, and arenot magnified. The pixels of contemporary x-ray imaging detectors arefar too large to resolve the proximity images. Instead, the inventiondisclosed here comprises a scintillator to convert the x-rays to opticalphotons, and then magnifies this optical image.

In order to achieve a particular resolution, there may be thicknessspecifications for the scintillator. For a resolution of 1 micron, forexample, the scintillator may have a specified thickness between 1 and10 microns. For thin scintillators, some of the incident x-rays willpass through the scintillator without being absorbed. Therefore, thequantum efficiency of this conversion process may worse than the PPMsystem, emitting visible photons for approximately 20% of the x-rayspassing through the scintillator. Beyond this, the microscope may loseadditional photons, depending on the optical system NA and the quantumefficiency of the visible CCD detector. However, even with these losses,the benefit provided by the higher flux of the extended source stillprovides a significant advantage.

Advantages of the Invention: Imaging Resolution.

The resolution of the prior art PPM system is determined by the spotsize of the x-ray source. For example, a source with a 1 micron spotsize will produce images with 1 micron resolution, assuming the systemis operating at optimal resolution. Practically speaking, it isdifficult to achieve resolution much below 1 micron with a PPM system,due to rapidly decreasing efficiency of the x-ray source for small spotsizes. As the spot size of the x-ray source decreases, the x-ray powermust be reduced to avoid melting the x-ray target. Furthermore, thex-ray target must be made thinner, to reduce scattering in the target.As a result, for each 2× decrease in spot size, the flux from the sourcedecreases a factor of about 10×.

For the imaging system according to the invention, the scintillator isin close proximity to the object being examined, and photons emitted arein proportion to the x-rays. For the optical system that relays thephotons emitted by the scintillator to the detector, assuming ascintillator emission wavelength of λ=535 nm and a solid immersionoptical system with NA≈1.75 comprising LuAG optical elements withrefractive index n=1.84, the definition for the diffraction-limitedresolution R of the optical system relaying scintillator photons to thedetector is:

$R = {\frac{\lambda}{2*{NA}} = {\frac{535\mspace{14mu}{nm}}{2*1.75} = {153\mspace{14mu}{nm}}}}$which is 6.5 times smaller than the 1 micron resolution of the PPMsystem.

Resolution is not only limited by the optical system, however. Whenusing an extended source, as with the PPM system, distortion and blur inthe projected shadows can still occur. FIG. 30 illustrates a systemaccording to the invention with a geometric projection of x-rays from anextended source 101-E of width S onto an object 200-A with two apertures221 separated by a distance A. The distance from the extended source101-E to the object 200-A is given by D, and the distance from theobject 200-A to the scintillator 310 is given by L. Depending on theratio of L and D, some magnification can occur, so in a preferredembodiment, D is much greater than L, and L is typically 1 mm orsmaller. In some embodiments, L will be 100 microns or smaller, with thescintillator placed as close to the object as practically possible. Insome embodiments, L will be 0 microns, and the object 200-A andscintillator 310 or scintillator assembly 300 will be in contact.

The bright spots of x-rays 321 on the scintillator 310 that correspondto the apertures 221 will have some blur 322 at the edges, depending onthe size S of the extended source 101-E and the distances D and L. Thetwo spots with separation A can be resolved if

$A \geq {\frac{L}{D}S}$For L=100 μm, D=10 cm, and S=1 mm, the minimum resolvable distance A=1μm, comparable to the PPM system. For L=25 μm, D=10 cm, and S=0.5 mm,the minimum resolvable distance A=125 nm, smaller than the estimatedresolution of the optical system.

In general, as a practical matter, a system will have adequateresolution if the contrast between two adjacent black and white objects(a line and a space) produces a modulation transfer function (MTF)greater than 5%

Clearly, these parameters can be optimized for certain circumstances andembodiments, as can the design of the optical microscope system, toproduce a system with high-resolution at high speed while minimizingcost.

Advantages of the Invention: Time to Market.

The high speed at which non-destructive images at resolutions smallerthan 50 microns can be gathered can improve the time to market for thedevelopment of manufacturing processes such as the flip chipinterconnect (FCI) process described earlier. The destructive processesfor failure analysis, also described earlier, can take weeks to collecta single image, and months to acquire statistical data on parts. Becauseof the rapid time in which images can be collected and analyzed usingthe system of the present invention, process development time for suchproducts can be counted in days, and is typically a fraction of thetotal time required to design and bring to market a new product.

Furthermore, because of the enhanced resolution, the present inventioncan be used for the new FCI processes with pitches smaller than 50microns. The present invention can be used for significantly smallerpitches, and still maintain the desired image resolution and speed.

In terms of the product development cycle, an increase in time forfeedback of one to several weeks has a distinct and significant impacton the time required to develop a new product. In a simple case, perhapsthree to five cycles of setup and data collection may be sufficient toestablish a process for a new device. In a more complex case, such as ahigh-density interposer or a 3D IC, tens or hundreds of iterations maybe required. Without the present invention, each of these cycles maytake several weeks, and the total time to market of the product may cometo be dominated by these cycles. Clearly a method of determining thequality of fine pitch (50 microns and smaller) bonds at the time ofprocessing offers a significant advantage.

The images and calculations produced by the system and methods disclosedherewith allow the quality of bonds to be examined immediately afterbonding in a matter of seconds or minutes.

In order to develop and qualify a new semiconductor product for massproduction, many individual processes and the integration of theseprocesses must be established, tuned, and tested. In the case of forminga through-silicon via (TSV) in a semiconductor wafer, the process flowtypically requires that the vias be formed first and the capture pads besubsequently formed on the wafer surface over the vias. Since thecapture pads obscure optical inspection of the vias themselves, in theabsence of the present invention, the alignment between the vias and thecapture pads may not be accurately determined at the time ofmanufacturing without cutting the silicon wafer and inspecting thisfeature in cross-section. Since this procedure is time consuming andalso destroys the silicon wafer and any economic value contained withinit, it is therefore undesirable.

In the case of bonding two or more chips or substrates or even completewafers together using FCI, the alignment, bonding force, bondingtemperature, rate of heating, and rate of cooling among other factorsmust be tightly controlled. While control of manufacturing equipment andprocesses can enable some of the necessary control, inspection andmeasurement of features within the product that are not opticallyvisible may also be required. Without the use of the apparatus disclosedin this invention, assembled parts must be cross-sectioned in order tobe inspected. Given the fine pitch of the interconnect bonds and thevery large quantity of connections, this procedure can take severalweeks. Even so, typically only a very small subset of the totalinterconnect bonds may actually be inspected.

The inability to inspect bonds quickly can add significantly to thelength of time required to fine tune both individual process steps aswell as the integration of multiple process steps to create a finishedproduct.

For example, consider a case where 25 iterations of the bonding processare required to develop and qualify a product. In the case without theapparatus disclosed in this invention, each iteration may require 1 weekto build each group of samples under various process and toolingconfigurations. After manufacturing a group of samples, an additional 2weeks may be required to cross-section individual units and inspect thequality and attributes of the bonds that have been created. The totaltime is therefore:25 cycles×(1 week making+2 weeks inspection)=75.0 weeks.

With the use of the apparatus disclosed in this invention, the 2 weeksof inspection can be reduced to a few minutes by eliminating the needfor time consuming cross-sectioning. The total time for the sequentialcycles may now be calculated as:25 cycles×(1 week making+1 hour inspection)=25.15 weeks,a reduction by 49.85 weeks (or 66% of the initial time to market).

With high-volume consumer electronic devices such as mobile phonesselling in volumes of more than 100 million units a year, it can beeasily seen that a decrease in time to market by 50 weeks (almost oneyear) can have significant impact on the market.

The apparatus may further be integrated into the bonding tool or viafilling tool, for example the electrochemical deposition tool, toprovide feedback to the bonding process in real time. The use of theapparatus in this way reduces time to market by many weeks and may infact enable a product to enter the market that otherwise would be toocostly or too late to market to have economic value.

Advantages of the Invention: Product Yield and Cost.

Currently, active silicon devices mounted onto a fine pitch siliconinterposer with a bump pitch of around 50 microns have beendemonstrated, but have not achieved high volume manufacture oracceptable yields. A well known case at this time is the Xilinx Virtex 7chip. This chip has 4 homogeneous processors mounted onto one siliconinterposer<http://www.xilinx.com/products/silicon-devices/3dic/index.htm>. Theapplication of this device is in high-speed network processors, whereselling prices are at the very highest end of the semiconductor market.It has been reported that commercial production began on these deviceswith overall yields related to package assembly and interconnect in therange of 80%. This yield is far lower than typically accepted in thesemiconductor field, and there is considerable additional costassociated with the scrap material. However, this particular part wasdetermined to have such high commercial value that, even considering thecost associated with low yield, it was commercially feasible to producewith only 80% package assembly yield.

In other lower-cost, more consumer-oriented segments of the market,pressure on pricing is much more intense, and it is unlikely that aproduct with package assembly yields at this level could be commerciallyviable. For this reason, it is necessary for the manufacturing processto be highly capable and tightly controlled, such that the amount ofscrap product or yield loss resulting from the bonding process isreduced. Traditionally, package assembly yields are in the 98 to 99%range. Those skilled in the art will quickly realize that scrapping goodchips by using poorly yielding bonding techniques, and packaging yieldsof 80% for lower value chips, are simply not acceptable.

It should be noted that, in the case of multiple dice mounted togethereither as a 3D IC or onto a high-density interposer, the failure of oneconnection on any chip will result in the scrapping of the entire MCP orpackage assembly. There may be thousands or tens of thousands ofconnections that must all function as designed. It is rare that any kindof rework or recovery of materials can be accomplished if any of thebonds are not produced correctly.

For example, take the case when a processor chip with a cost of $10 ismounted together with four memory chips costing $5 each, or $20. Thetotal cost of the chips is therefore $30. Chip assembly and packagingmay add another $5 of cost for a total assembly cost of $35.

In the case where the assembly yield for these parts is 80%, for each100 sets of chips, 20 will be scrapped. The manufacturing cost for 100units is given by:Cost=[$10+(4×$5)+$5]×100=$3,500.However, with only 80% of the assemblies being functional, the totalcost per working assembly will be:

${{Cost}/{unit}} = {\frac{{\$ 3}\text{,}500}{80} = {{\$ 43}{.75}}}$which is 24% more expensive than a process yielding 99% would provide.This cost increase may consume the entire profit margin for some low-endproducts, and in any case represents an undesirable outcome.

By using the images and measurements produced by the apparatus in thisdisclosure, the processes of aligning, inspection bonding can becontrolled and monitored such that the yield can be rapidly increased.For MCP packages, in the example above, detecting a flaw between thefirst two dice will allow the packaging assembler to scrap the first twodie only, and not require the loss of all five dice, therefore savingscrap costs and improving yield. It is common for well-controlled andmonitored assembly processes to have yields of over 99.9%. The presentinvention allows a packaging assembler to achieve a yield of greaterthan or equal to 90% in MCP structures having more than 4 dice andhaving more than 100 TSVs per interposer or die layer at pitches wherethe smallest pitch is less than 100 microns. The same yield advantagemay be achieved in the flip chip configuration having more than 400microbumps at a pitch where the smallest pitch is less than 100 microns.

This same advantage in cost and yield can be seen at other steps in themanufacturing process for fine-pitch interposers and 3D die stacking,such as via fill monitor for voids, via capture pad alignment to via,alignment of chip-bump to chip or interposer pad, and quality ofcompleted joint after bonding. It may also be used to measure bondlinein the assembly of multiple slices of silicon devices or fine pitchinterposers or between silicon devices and other materials of interestwhere this bondline thickness is critical to device performance.

EMBODIMENTS AND LIMITATIONS

With this Application, several embodiments of the invention, includingthe best modes for various circumstances, have been disclosed. Whilespecific materials, designs, configurations and fabrication steps havebeen set forth to describe this invention and the preferred embodiments,such descriptions are not intended to be limiting. Modifications andchanges may be apparent to those skilled in the art, and it is intendedthat this invention be limited only by the scope of the appended claims.

We claim:
 1. A system for forming x-ray images, comprising: a source ofx-rays; a movable mount for the source of x-rays; a mount for holding anobject positioned such that x-rays from the source are aligned toilluminate an object held in the mount at an angle of incidence withrespect to the object; a scintillator that absorbs x-rays and emitsvisible photons; an optical system that forms an image of thescintillator; and a detector for converting the image of the emittedphotons into electronic signals; wherein the emission of x-rays occursfrom a spot with a diameter greater than 10 micrometers formed by thecollision of an electron beam with an anode; and the ratio of the spotsize of the x-ray source and the resolution of the optical system isgreater than 20; wherein the mounted source of x-rays is configured tobe positioned to change the angle of incidence of the x-rays withrespect to the object.
 2. The imaging system of claim 1, wherein theratio of the spot size of the x-ray source and the resolution of theoptical system is greater than
 100. 3. The imaging system of claim 1,additionally comprising a recorder for the electronic signals.
 4. Theimaging system of claim 1, wherein the scintillator comprises LuAG. 5.The imaging system of claim 1, wherein the scintillator has a thicknessof less than 50 micrometers.
 6. The imaging system of claim 1, whereinthe detector for converting the image of the emitted photons intoelectronic signals comprises a charge-coupled device (CCD).
 7. Theimaging system of claim 3, additionally comprising a system controllerthat controls: motion of the mount for the source of x-rays, motion ofthe mount for holding an object, and the recorder for the electronicsignals corresponding to the image of the emitted photons.
 8. Theimaging system of claim 7, wherein the system controller also controls:properties of the x-ray source selected from the group consisting of:x-ray source angle, x-ray source power, x-ray source energy, and x-raybeam shape; and properties of the optical system selected from the groupconsisting of: optical system focusing, optical system magnification,and x-ray image collection.
 9. The imaging system of claim 1, wherein anobject is placed in the mount for holding an object.
 10. The imagingsystem of claim 9, wherein the object is selected from the groupconsisting of: a silicon interposer, a silicon dioxide interposer, anintegrated circuit, a printed circuit board, a 3D IC package, a 2.5D ICpackage, and a multi-chip-module.
 11. The imaging system of claim 9,wherein the object comprises through-silicon vias.
 12. The imagingsystem of claim 9, wherein the object comprises solder bumps.
 13. Theimaging system of claim 9, wherein motion of the mount for the source ofx-rays is controlled to change the angle of incidence the x-rays withrespect to the object.
 14. The imaging system of claim 1, wherein theoptical system comprises a microscope objective.
 15. A system forforming x-ray images, comprising: a source of x-rays; a movable mountfor the source of x-rays; a mount for holding an object positioned suchthat x-rays from the source are aligned to illuminate an object held inthe mount at an angle of incidence with respect to the object; ascintillator that absorbs x-rays and emits visible photons; an opticalsystem that forms an image of the scintillator; and a detector forconverting the image of the emitted photons into electronic signals;wherein an object is placed in the mount for holding an object; andwherein the scintillator and the object is are separated by a distanceof less than 1 mm; and wherein the mounted source of x-rays isconfigured to be positioned to change the angle of incidence of thex-rays with respect to the object.
 16. The imaging system of claim 15,wherein the scintillator assembly and the object are in contact.
 17. Theimaging system of claim 15, wherein the distance between thescintillator and the object is less than 100 micrometers.
 18. Theimaging system of claim 15, wherein the emission of x-rays occurs from aspot formed by the collision of an electron beam with an anode; and theratio of the spot size of the x-ray source and the resolution of theoptical system is greater than
 20. 19. The imaging system of claim 15,wherein the scintillator comprises LuAG.
 20. The imaging system of claim15, wherein the scintillator has a thickness of less than 50micrometers.
 21. The imaging system of claim 15, wherein the detectorfor converting the image of the emitted photons into electronic signalscomprises a charge-coupled device (CCD).
 22. The imaging system of claim15, additionally comprising: a recorder for the electronic signals; anda system controller that controls: motion of the mount for the source ofx-rays, motion of the mount for holding an object, and the recorder forthe electronic signals corresponding to the image of the emittedphotons.
 23. The imaging system of claim 22, wherein the systemcontroller also controls: properties of the x-ray source selected fromthe group consisting of: x-ray source angle, x-ray source power, x-raysource energy, and x-ray beam shape; and properties of the opticalsystem selected from the group consisting of: optical system focusing,optical system magnification, and x-ray image collection.
 24. Theimaging system of claim 15, wherein the object is selected from thegroup consisting of a silicon interposer, a silicon dioxide interposer,an integrated circuit, a printed circuit board, a 3D IC package, a 2.5DIC package, and a multi-chip-module.
 25. The imaging system of claim 15,wherein the object comprises through-silicon vias.
 26. The imagingsystem of claim 15, wherein the object comprises solder bumps.
 27. Theimaging system of claim 15, wherein motion of the mount for the sourceof x-rays is controlled to change the angle of incidence of the x-rayswith respect to the object.
 28. The imaging system of claim 15, whereinthe optical system comprises a microscope objective.
 29. The imagingsystem of claim 15, wherein the optical system has an optical axis; andadditionally comprising a source controller for adjusting the positionof the source of x-rays such that the source spot of the x-ray emitterwithin the source of x-rays is not on the optical axis.
 30. A method forconducting metrology of an object, comprising: selecting an object formeasurement; forming at least one image of the object using a systemcomprising: a source of x-rays; a movable mount for the source of x-raysa mount for holding an object; a scintillator that absorbs x-rays andemits visible photons; an optical system that forms an image of thescintillator; detecting the image of the scintillator; converting thedetected image into electronic signals; storing the electronic signalscorresponding to the image; analyzing the electronic signalscorresponding to the image with a predetermined recipe; determining atleast one physical dimension for the object; and displaying the at leastone physical dimension.
 31. A method for conducting inspection of anobject, comprising: selecting an object for inspection; forming at leastone image of the object using a system comprising: a source of x-rays; amovable mount for the source of x-rays a mount for holding an object; ascintillator that absorbs x-rays and emits visible photons; an opticalsystem that forms an image of the scintillator; detecting the image ofthe scintillator; converting the detected image into electronic signals;storing the electronic signals corresponding to the image; analyzing theelectronic signals corresponding to the image with a predeterminedrecipe for identification of defects; and displaying the results of thedefect analysis.
 32. A system for forming x-ray images, comprising: asource of x-rays; a movable mount for the source of x-rays; anadjustable mount for positioning an object to be illuminated at an angleof incidence with respect to the object by x-rays from the x-ray source;a scintillator that absorbs x-rays and emits visible photons; an opticalsystem that forms an image of the scintillator; and a detector forconverting the image of the emitted photons into electronic signals; andwherein the optical system has an optical axis; and additionallycomprising a controller for adjusting the position of the source ofx-rays such that the source spot of the x-ray emitter within the sourceof x-rays is not on the optical axis of the optical system.
 33. Theimaging system of claim 32, wherein the emission of x-rays occurs from aspot formed by the collision of an electron beam with an anode; and theratio of the spot size of the x-ray source and the resolution of theoptical system is greater than
 20. 34. The imaging system of claim 32,wherein the scintillator is has a thickness of less than 50 micrometers.35. The imaging system of claim 32, wherein the angle of incidence ofthe x-rays with respect to the object is adjustable.
 36. The imagingsystem of claim 32, wherein the optical system comprises a microscopeobjective.
 37. A system for forming x-ray images, comprising: a sourceof x-rays; a scintillator that absorbs x-rays and emits visible orultraviolet photons; an optical imaging system that forms an image ofthe scintillator; and a detector for converting the image of the emittedphotons into electronic signals; wherein the emission of x-rays occursfrom a spot with a diameter greater than 10 micrometers formed by thecollision of an electron beam with an anode; the resolution of theoptical system is greater than 1 micrometer; and the ratio of the spotsize of the x-ray source and the resolution of the optical system isgreater than
 2. 38. The imaging system of claim 37, wherein the ratio ofthe spot size of the x-ray source and the resolution of the opticalsystem is greater than
 5. 39. The imaging system of claim 38, whereinthe ratio of the spot size of the x-ray source and the resolution of theoptical system is greater than
 10. 40. The imaging system of claim 37,wherein the scintillator comprises LuAG.
 41. The imaging system of claim37, wherein the scintillator has a thickness of less than 50micrometers.
 42. The imaging system of claim 37, wherein the detectorfor converting the image of the emitted photons into electronic signalscomprises a charge-coupled device (CCD).
 43. The imaging system of claim37, wherein an object to be examined is supported by the scintillator.44. The imaging system of claim 37, additionally comprising: a supportstructure for an object; and a system controller that controls motion ofthe support structure for an object.
 45. The imaging system of claim 44,wherein the system controller also controls: properties of the x-raysource selected from the group consisting of: x-ray source angle, x-raysource power, x-ray source energy, and x-ray beam shape; and propertiesof the optical system selected from the group consisting of: opticalsystem focusing, optical system magnification, and x-ray imagecollection.
 46. The imaging system of claim 37, wherein the opticalimaging system comprises a microscope objective.
 47. The imaging systemof claim 37, wherein the optical imaging system comprises a fiber opticbundle.
 48. The imaging system of claim 44, wherein an object is placedin the support structure for an object, and is positioned such thatx-rays from the source illuminate the object at an angle of incidencewith respect to the object.
 49. The imaging system of claim 48, whereinthe angle of incidence of the x-rays with respect to the object isadjustable.
 50. The imaging system of claim 48, wherein the object isselected from the group consisting of: a silicon interposer, a silicondioxide interposer, an integrated circuit, a printed circuit board, a 3DIC package, a 2.5D IC package, and a multi-chip-module.
 51. The imagingsystem of claim 48, wherein the object comprises through-silicon vias.52. The imaging system of claim 48, wherein the object comprises solderbumps.
 53. The imaging system of claim 37, wherein the optical systemhas an optical axis; and additionally comprising a source controller foradjusting the position of the source of x-rays such that the source spotof the x-ray emitter within the source of x-rays is not on the opticalaxis.
 54. The imaging system of claim 38, wherein the scintillator andthe object is are separated by a distance of less than 1 mm.